I'd be interested in a free roam mode if it were done correctly, but my version of "correctly" is likely very different from everyone else.
What I would NOT want to see is anything like Midnight Club and similar games. I don't have any problem with those types of games in and of themselves, I just don't think that type of thing has a place in a Gran Turismo game is all. Leave that in the capable hands of the companies / game franchises that already do it.
What I would be interested in is a free roam mode that is something more akin to Euro Truck Simulator 2, ok stop laughing I'm serious
. Essentially it would be a realistic but simplified road system that connects the various track locations around the world, with a rudimentary set of traffic laws and obnoxiously large fines that are metered out automagically if you break them (things like speeding in certain areas, running red lights, hitting other vehicles, etc) and possibly even having your current car impounded if you break too many.
There would be no actual racing involved but if you wanted to you could have your car shipped to Silverstone, then drive down to Dover and hop on a train to Calais and drive over to Le Mans for example.
It could even be used as an expanded Photo Mode too with the option to drive to a "beauty spot" to take some pictures or record a bit of replay footage instead of just picking a location from a catalogue.
Heh I guess in a way it could end up like that PSN Home thing.. bunch of roads and air / sea transport areas that link various portals for tracks, photo mode locales, GT Auto garages and such. If you want to putter around Europe visiting race tracks you can, or just use the menus like do currently and ignore Free Roam completely.