I am probably wrong but I wanna get credit if I am right. Hence this post.
I don't think we are getting a new Mac Pro.
Instead, I have two thoughts.
1) Apple introduces new prosumer apps on the iPad and Mac that leverage cloud computing to speed up computations. There are already apps that do similar things, the iTunes store sorta works this way, as does Siri (or at least it used to, not sure if it still does). This way, every single Mac and iPad out there becomes the "Pro" model.
2) Introduce the new Mac mini as a beefed up "thin client" (thick client?), the job of which is mainly to connect to cloud servers that again speedup computations. This requires some more software magic than I understand but I think it is workable in theory. There is no reason the Mac mini, with up to date hardware, couldn't be a competitive computer. It has a cute form factor and space to put in decent parts.
Why would Apple do this, well Amazon and Msft have done well in this space, and it makes them a lot of money. It's more portable. I really don't think Apple wants to be in the brick that sits on your desk all the time business anymore. This is a solution that can be applied to every computer they have.
The biggest hitch here is latency and privacy, since alot of information would have to be sent to Apple's servers. Privacy can be handled through encryption, though I am not sure how efficiently this would work.