I think it may be an improvement. The question I cannot answer (yet) is whether it will be enough of an improvement. Is the bare (sans electronic gizmos) 991chassis much better than the current 997?. If so then there will be a marked improvement, if not, then bring on the 961 ASAP. (It is my understanding that one of the main issues (there are others) with the rear engine layout is getting the balance of the car right).
The other problem is engine. Can the Porsche flat six compete with the 458 V8? . It should be Porsche's objective to have an engine that can compete with the 458's engine without resorting to BoP in order to make it competitive,
I am sure Porsche could eventually get a waiver to move the engine, but that really defeats the purpose of racing in the GT class. These cars are supposed to be based on the road going versions of the same car. Porsche likes this type of racing, precisely because it is so closely associated to their road going products. (although I sometimes wonder about its effectiveness. Just look and see how many on this forum (mostly 911 owners) take any interest in sportscar racing)
There really is no point in taking the BMW route and racing what is essentially a prototype against other GT cars.
Lets see how this evolves - Unfortunately we will never know what is really going on (and what the thinking is ) behind the scenes.