I think GT5 was lacking in GT type cars a bit. Other than that, I trust PD an make a good line up of cars for GT6. I'm more interested in tracks anyway.
In terms of tracks, what I'd like to see is a better variation of off-road tracks, perhaps including some actual rally stages could do the trick and adding in rallycross as a discipline is something I'd definitely be prepared for. Supposing PD keeps its NASCAR license, I'd love to see them add some more good ovals, both with and without roadcourses attached, regardless of whether NASCAR even uses them for the Sprint Cup or at all. What GT has so far also lacked are actual street circuits, and I'd love to see some of those. Lastly, I'd love to see some tracks based in the Netherlands, even if they're fictional.
But now, without further ado, my wishlist:
All GT5 tracks including Spa and Motegi
Tracks and layouts used in the series that weren't in GT5:
-Circuit Ricardo Tormo/ Circuit de Valencia
-Fuji Speedway 90's and 80's
-Sonoma Raceway (formerly Infineon)
-Suzuka west
-Apricot hill
-El Capitan and the Cathedral Rocks Trials
-Opera Paris
-Hong Kong
-Rome circuit in GT2/3 layout
-SSR11 in GT1 layout
Layouts which are available at tracks in the series but never used (including proper kart tracks):
-Monza Junior, Oval and Combined (you know you want to) as well as rally stages
-Le Mans Bugatti, Maison Blanche and Kart
-Daytona Motorcycle (why not?)
-Fuji Speedway gymkhana, drift and kart tracks
-Indianapolis 2008-onwards roadcourse, clockwise without turn 1 infield and anticlockwise with turn 1 infield
-Nurburgring South short track
-Spa kart (has a separate name but can't come up with it atm)
-Sonoma Indy, dragstrip and kart
-Suzuka West and kart
-Motegi kart
-Monaco kart (various layouts)
Rallycross tracks (3 to start things off):
-Eurocircuit Valkenswaard
-Lydden Hill (also roadcourse and even "oval")
-Nyirad (also dirt track)
Ovals for NASCAR use (only as much as required for superb line-up):
-Raceway Venray (please?)
-New Hampshire Motor Speedway (also roadcourse)
-Bristol Motor Speedway (also dragstrip)
-Phoenix International Raceway (don't know if the roadcourse is still usable)
-Las Vegas Motor Speedway (also all roadcourses, the short ovals and dragstrip)
-Eurospeedway Lausitzring (including DEKRA testoval as a possible replacement for driving park and SSRX)
-California Speedway (including roadcourses)
-Pocono Raceway (including roadcourses)
Real street circuits:
-Rome Formula E Circuit to be used starting 2014 (uses main straight of Rome GT2/3 but goes left instead of right, can be combined with Rome GT2/3 and Rome GT5 to a track some 6 km in length depending on exact layout)
-Surfers Paradise Indy long and V8 Supercars short track
-Norisring
-Circuito da Boavista/Oporto
-Guia Circuit/Macau
-Long Beach Grand Prix
-Circuit Gilles Villeneuve/Montreal
Real world roadcourse:
-Circuit Park Zandvoort (Including two shortrally stages)
-Autodromo do Algarve/Portimão
-Potrero de los Funes
-Mont Tremblant
-Silverstone (including Stowe circuit)
-Brands Hatch
-Imola
-Motorland Aragon (including all the other tracks on site)
-Redbull Ring
-Sepang