I believe the Ferrari Dino was spotted in early GTS Scape screens, and some additional specific Lamborghini models (that weren't yet in the game) were spotted in the credits. There was also the bugged menu with a '91 NSX posted somewhere, so those could be added up if the screens are to be believed. Then in addition to the SEMA cars there's also Peddle Beach winners that are supposed to be showing up at some point in GT's future, whether or not it happens in GT Sport remains to be seen though.
Also on the track side we have confirmation of Deep Forest being in development but no ETA. Other tracks that have been in some way alluded to include Le Mans (scapes since day one and in fairly early promotional material), Autopolis (behind-the-scenes shots of PD headquarters showed early development/debug versions of the circuit before GTS's launch), Barcelona (A GTS esports event is being hosted at the circuit during a real 24hr race in September), and Seattle (the name appeared by mistake at the Copperbox unveiling event), as well as additional layouts to several of the GT-originals - however, none of these are officially confirmed to be under development for GT Sport. Le Mans is likely given the scapes (and therefore likely PD's scanning team for the location), and Autopolis has actual footage available, but we have no idea if the assets were scrapped or if licensing issues have come up since it's 2016 "leak". There's no confirmation for any new layouts to be added to the existing circuits, but someone found "secret" Kyoto layouts hidden on the GTS website, infield layouts of Northern Isle are already available in the campaign mode, and people have been theorizing about a few potential connecting roads on Alsace.
