PD has sold more than 65 Million copies of the GT franchise, and I hardly think that PD would move to develop an arcade title because their target market (us) actually buy the game as opposed to NFS series etc.
PD isn't lacking revenue or sales, maybe Sony could be - but that won't have anything to do with PD.
I see no sense in making a move like that; but then again this is just your speculation and I hope it will stay that way...
If PD was to make an arcade game, it wouldn't be called GT6 and now this makes it a bit off topic.
GT5 was called Driving Simulator for a reason - because it's the closest simulator you can get on the PS3; and I think they'll continue this marketing whatever, and attach it to the next game in the series too. It will have improved (the older games in the series show the evolution).