Rally needs a course creator to be viable. PD don't have the bandwidth to do anything on the level of DiRT Rally. The whole point of rally stages/racing is a level of unpredictability. If you are doing the same 5 tracks over and over again, with the same conditions... it's not really rally.
Yeah, I really liked the randomly-generated courses of GT5's Special Event for rally.
Otherwise, I think rally should stay, as it's been a part of GT for too long. I personally would hope Gr.B gets expanded with more real-world Group B rally cars from prior GT games like the Peugeot 205 T16, Citroen BX 4TC, Renault 5 Maxi Turbo, Mitsubishi Starion 4WD, Nissan 240RS, and Lancia Delta S4, with additions from other automakers like Porsche, Ferrari, BMW, and other potential automakers like MG. Some automakers could even have multiple options, as Ford could potentially have the Mustang and Focus Gr.B, but also the RS200. Another example was Lancia, if it gets both the 037 and the return of the Delta S4, and then Audi could have both iterations of the Quattro from GT6, as only the Pikes Peak version of the Quattro returned for GT Sport. Then, perhaps, there could also a "Gr.C" for pre-Group B rally cars, like the Lancia Stratos and Nissan Bluebird, as well as a group for post-Group B rally cars like the Suzuki Escudo, the Citroen C4 WRC, or the Tajima E-Runner.
I think having an interesting, perhaps even anachronistic group of cars in the same class is part of both Gran Turismo itself, and what makes its events fun to both participate in and spectate. The Gr.3 class is a good example of this, with made-for-game race cars, FIA GT3, a GT car from the mid-90s, a FIA GT1 car from the late 00s, and GTE cars, with Super GT300 cars being a likely fit as well.