Apple has bounced between nVidia and ATI/AMD many times over the years, so it's perfectly reasonable to expect that it will happen again - if it suits their design goals.
Nvidia's Maxwell architecture focuses on power efficiency and low heat, so physically it would be a good match. Mac Pros have historically been offered with BTO options for ATI and Nvidia cards in the same generation, so there is precedent for that. Only big question (as others in this thread have mentioned) is OpenCL.
Nvidia's Maxwell architecture focuses on power efficiency and low heat, so physically it would be a good match. Mac Pros have historically been offered with BTO options for ATI and Nvidia cards in the same generation, so there is precedent for that. Only big question (as others in this thread have mentioned) is OpenCL.
Kepler is already generally better than AMD's offerings from a power efficiency and heat standpoint - Maxwell even more so. Cost is likely the main thing. I'd imagine AMD probably severely undercut nVidia on price. It makes perfect sense as a move to try to revive the FirePro brand.