One idea that occurred to me was based on the recent revitalization of the Darkmoon Faire, which offers content that is accessible for one week out of a month. What if there were a couple of raid bosses that were like that? They could be attached to the Faire or be entirely their own separate experiences, but the important thing would be for there to be raid content that was available once a month rather than once a week. You wouldn't want to put any BiS gear on that kind of raid, but one can easily imagine its being a raid encounter with a lot of potential for unconventional loot: pets, mounts, even cosmetic items. In a way, that kind of encounter is more likely to retain relevance into the future. Tune it up every time a new expansion launches, and people will keep running it indefinitely.
Another possibility is the timed raid. You can go with either the ZA timed run model or the Algalon model. You get extra rewards if you complete it within the timer, or even more extreme, the timer determines whether or not you even can
complete the encounter. With raid sizes being smaller (and as far as we know, staying that way), you could even design an entire two-encounter raid like Gruul's Lair with a two-hour timer, and let folks have at it.
There's no reason to limit ourselves, however. Another potential model for raid lockouts could be a daily reset. The current tier 11 raids give gear that's technically obsolete right now and not as powerful as drops from the Hour of Twilight heroic 5-mans. Imagine if they were added to Raid Finder on a daily reset. You wouldn't even need to change the encounters at all; simply allow people to farm those outdated raids for tier pieces and transmog weapons.
The real point is, the paradigm of a weekly reset isn't necessarily the only one and hasn't been even in WoW
's own history. Mixing in different resets seems like one way to give people more options in terms of what content to run, which is so far the successful model for Cataclysm
World of Warcraft: Cataclysm has destroyed Azeroth as we know it; nothing is the same! In WoW Insider's Guide to Cataclysm, you can find out everything you need to know about WoW's third expansion, from leveling up a new goblin or worgen to breaking news and strategies on endgame play.