There are two specific games that have helped inspire this idea: one is Call of Duty 4 and the other is Guild Wars. The former has a wonderful leveling feature that creates a system where experience and ranking up matters and it avoids getting into statistics nightmare. Whereas the second washes its hands of a reoccurring subscription model in favor of occasional platform expansions. These two features are essential for dramatically reducing the barrier to entry felt by many potential players.
I grappled with the issue of making the current style and setting of Rock Band into an MMO for quite a stretch of time. It wasn't until I finally realized the appeal of infusing more fiction into the game that something clicked. Anyone familiar with the history of rock 'n roll knows that various aspects of the wide-reaching genre easily mesh into things like undead, dragons, demons and tons of other mythical creatures. However, music takes a fiercely different kind of ownership with these classic creatures. One look at developer Double Fine's upcoming game Brutal Legend tells us with the utmost certainty that there's a demand for games that explore fantasy worlds where all kinds of rock music battle various forms of evil. That's not to say that sci-fi should be left out of the equation. I'd love to battle psychotic robots and evil mutant bears armed with laser eyes, too.
The approach I would take is to fashion an alternate-Earth where the primeval power behind the origin of music (not just rock) that was once shackled to the planet's core is unleashed upon the world once more. This shapeless power seeps into everything and creates portals to the underworld where no such thing existed before. It turns regular wildlife into vicious monstrosities that roam for flesh and bone to gnaw upon. Of course, the revival of primeval music means songs which once moved thousands of people can now perform even greater and amazing feats of power. Massive drum fills can shake the very foundation of the earth, blazing guitar riffs can conjure electrical energies and powerful vocals can shatter anything in its path. You know, the kind of stuff that can decimate sinister monsters or enemy musicians alike.
This world should pull from all sorts of places, not just Nordic rock legends. I want to see cybernetic slaughter squads trained in the way of the ninja and rocking out to Japanese power metal. Or how about Southern Rock demons wailing on guitars made of brimstone, bones and ablaze with unearthly fire? The possibilities are endless.
Emphasis on a tangible world that characters exist within is important to any MMO for a multitude of reasons -- the biggest being it greatly aids in creating a sense of persistence. That said, not every MMO needs to have an avatar moving across vast reaches of virtual space to work. How would anyone move their little avatar around with a plastic guitar or drum set anyhow? I really don't want to see a thumb-stick protruding out all my instruments.
In a game about playing instruments, you want to let players get to the action as quickly as they can. So, there are only three places where a player's avatar really matters: during group play, to other guildmates and during PvP bouts. The creation of a world with a lore, style and setting is a start. Everyone will see each other when playing a song, taking care of group play in both PvE and PvP situations. Lastly, a guild window should display the current appearance of someone's character and all information regarding it.
After that it's simply a matter of creating a instrument-friendly map and menu system that constantly reminds players it's a living, breathing world. The best way to do this would be to create a PvP system that allows player to capture chunks of the game world by battling enemy guilds. Desirable rewards would need to be thought up, of course.
A Rock Band MMO should still retain its core gameplay, but with an addition I've always wanted: battles. I don't mean the kind of battles where notes are doubled or certain note buttons are disabled by opposing players. Instead what I'd like to see is a fantasy-fueled extension of the current system. A heavy statistics game this isn't, basic ideas like band health and energy earned from white notes should remain -- and instead be built upon. A big addition I'd like to see are active and passive powers that actually appear and animate within the game. No classes of course, think of it as a shared pool that all powers are picked from. Limiting players to a certain amount of slotted powers is essential to the design. Ultimately, it's a system that should make the on-screen action a crazy mix of fret-melting solos and face-melting trades of powers between you and monsters or opposing players.
I'll lay out an example or two. Say a guitarist equips "Live Wire Finish", which is an active offensive power that goes off at the end of a successful solo -- assuming that enough energy is present. When said guitarist completes their solo, a bolt of lightning explodes from their instrument with a thunderous crack. Upon zapping the intended targets, it lowers health proportionate to the quality of the solo. Different examples are a bassist shielding the band from an upcoming attack via "funktricity" or maybe a vocalist buffing the band's energy bars through a leadership power. All active powers would either come from finishing solos and fills or utilizing built up energy. Since vocalists only have the ability to use energy when it's offered, their powers would probably be bigger in effect.
As an aside, I like the idea of solos or fills being interchangeable with songs. So maybe an easier solo would shoot off a lesser power. The only problem I see with this is that it could really interfere with licensed music.
Customizing player functionality is only one side of a hundred-dollar coin. Being able to make your character stand out in cool and/or interesting ways is equally important. A powerful cosmetic customization system is nigh a requirement. To that end bits and pieces of instruments would be highly interchangeable and paint-able. I'm talking necks, pickups, knobs, sliders, whammy bars, the head, the body and that's just guitars. Moreover, characters themselves should start with wide options of facial customization. As time goes on things like hair, accessories and plenty of clothing should be made available. These would likely be cosmetic changes only, but functionality tweaks could be explored assuming it could be balanced.
Adding experience bars that are always represented on-screen will go a long way to keeping people hooked. As ranks are earned, both customization options and powers would unlock -- not to mention the stature of being a higher rank. The exact amount of ranks depends on how much there is to unlock and also whether unlockables are given solely through new ranks or also through beating difficult opponents in-game.
So why bother with all this Rock Band MMO conceptualizing? Everyone already spends vast, sprawling amounts of time playing the games. It only makes sense to add in components that reward behavior that's already present. Plus the constant stream of downloadable songs is already something of a subscription model -- albeit a voluntary one. This idea makes the concept of additional clothing, instrument and hair download packs an exceedingly more appealing option.
And let's not forget that non-MMO Rock Band experiences can keep coming out. The creation of a Rock Band-inspired MMO is more of an aside to the genre rather than a Point B, where all roads converge. Although, there's always the off-change that a game similar to the one I just laid out could become so wildly successful that something to that effect comes true.