We did have one in London in 2010 in December. The hostel we stayed in was cheap, but also turned out to be really not very nice at all. We did manage to settle on somewhere to eat quickly, but finding somewhere that suits everyone (we went to Wagamama as they accept bigger groups without booking easily, and suited the gluten free and dairy free people) can be difficult, as well as getting in if there is a big group of you
Well I spent a lot of time outside at G2G9 but quite frankly as I tend to have quite a drive to get to a G2G, I don't really want to get in a car agaien until I have to go home. Catching up with/getting to know people is what it is all about for me and that isn't easy to do out and about, although it does work on a day out G2G but then that's something different.
However, there is nothign to stop you organising such an event and people will join you if they are interested.
I think the main 'g2gs' will probably stay the way that they are - campsites/places where a group can self-cater etc. The very first g2g, fyi, was at a youth hostel, was for just one night and the menu an interesting problem! Most people preferred the options we were given when they thought we were all kids! The cost of it was about as much for one night as it tends to cost for a two night g2g arranged these days.
There is no reason at all why you can't arrange a hotel version if you want, but it would probably be a local version rather than the main g2gs due to the cost.