BCI input devices rushed out in relatively crude forms around the mid-eighties when microcomputers were really starting to get some traction. A number of biofeedback devices hit the market, along with several joysticks (and later even a couple of mice) based on simple galvanic receptors or post-synaptic electro-encephalographic receptors, and targeted at gamers.
Made for consumers (rather than medicine) the quality of the units weren't terribly high. The quality of actual signal detection could be charitably referred to as 'crude'. However, in the main, they did actually work, even though they were - at best - a little erratic.
It was a new age of computing, a brand new age of gaming, and kickass joystick interfaces you didn't need to move a muscle to use. Sure enough, people avoided them in droves.
Problem is, what you needed were two things. The first was a bundle of cash - these little babies weren't cheap. The second was training. These devices don't read your brain. Your brain, instead, has to rewire itself to use them properly. Actually, that's not so hard. It takes upwards of 30 or 40 hours, it's true - but the human brain is actually very good at this sort of adaptation.
Unfortunately the adaptation time goes way up the more inputs the unit has. A joystick and one button has quite a learning curve. Start slapping on the buttons and it can go up nearly exponentially - part of that is because of the crude receptors and circuitry that was used.
A few dedicated users got full value out of these things. It just wasn't enough to keep the businesses who were making them alive. Maybe a few hundred units sold. Likely very few of the people who bought them had the patience to work through the adaptation period.
Nonetheless, I've seen (and used!) some very good homebrew efforts made with medical-grade equipment. If you think the BCI joysticks of the 80's were expensive (they could easily cost more than the computer you were planning to hook them up to), well, you ain't seen nothin', honey.
Using off-the-shelf medical modules, leads, and modern ENOBIO receptors, you're looking at a cool 15 or 20 grand before you roll your sleeves up, grab the soldering iron, kick the hunchback and start laughing maniacally.
And BCI systems are kind of spooky.
Your BCI joystick picks up your decisions before you're consciously aware of having made the decision. Once you're usefully acclimatized to one, it's annoyingly a perceptible fraction of a second in front of your awareness.
People call that "creepy".
Modern experimentation aside - some fledgling startup could come along right now and produce BCI input devices tomorrow. They'd be expensive, they'd take you a long time to get used to, and short of electrocorticographic techniques (that's receptors directly against the brain - we call that invasive. Do not try this at home), they'd still be somewhat erratic.
So - what I'm wondering here is - would you use something like this for your MMO or Virtual World - or would you rather strap on your Powerglove (caution, link is not safe if you're allergic to the 1980s. May contain traces of nuts) and rock it out with the mobs?