Naturally, rock stars have guaranteed support in their hometown. Uematsu and FF are fortunately popular enough to be able to branch out into 'the west' and get some good recognition. There was a tour in the US in '05 called 'Dear Friends' where they went to various cities performing music from Final Fantasy.

Today, there is "Video Games Live" which takes music from various video games (not limited to Japan) and performs them in concert.

That said, the culture is different in Japan. In entertainment, particularly in anime as far as I know, there are "live events" that feature the voice cast of the anime. These are pretty popular events (naturally based on the anime's popularity), so there is already the idea of 'if they like your stuff, they'll come out for it'.

In the US (and I know the OP is not from the US) they're starting to spread that. Not so much for anime outside of conventions, but for games. For the Xbox360 games Dead Rising and Lost Planet, Capcom's Keiji Inafune was in new york signing copies of the game. It's a far cry from a full blown Mega Man concert (Inafune created Mega Man as well), but closer to the real-life fanservice that those kinds of events are.

That's what it really boils down to, fanservice. If there are enough fans to warrant something like this happening and to continue supporting it, then it's more likely to happen. Korea can have huge Starcraft tournaments in national stadiums--where people pay decent amounts of money just to spectate in the stands--with fireworks and million dollar prizes and such like that, because Starcraft is freaking huge in Korea. To use Korea again, they can hire Yoko Kanno (who is Japan's best composer*, sorry Uematsu) to make music for their game (Ragnarok 2) and then fly her to Korea to have a huge concert, because Ragnarok is freaking huge (and Kanno is a freaking goddess). Sufficient fanbase is the key.

Right now, "Video Games Live" is a pretty major project. It is a worldwide thing, with the most recent performance being in London. From what I understand it's very successful. By incorporating several different games instead of just FF, they have a much wider fanbase to draw into their crowd. I wouldn't worry about adults 'not taking it seriously', they have their audience and it's obviously not all-inclusive.

*opinion, duh