I think IBM said development would continue in the context of hybrid designs and next-gen architectures that carry some cell flavourings.
Honestly don't see what would be so outlandish or undesirable about a 'beefed up' Cell design - or - for example, a hybrid design with a few larger, newer, cores and an array of SPU compliant processors. 6 SPUs, with some tweaks, would be a fantastic for BC (obviously) and could do their bit for native PS4 applications alongside other main cores - and I have to guess would take up relatively little die area in 2013 (?) Reworked memory interfaces would help a lot there, IIRC it was holding back shrinkage to date, but they'd have the opportunity to revise that totally in a new system. They could probably clock them quite substantially higher too, for the benefit of PS4 code.
I have a feeling, though, that the new systems will have a higher focus on GPU processing power, a higher ratio of gpu:cpu than the current systems did. There may be relatively 'small' CPUs in the next systems.