At this point it's feeling exactly like the stretch where Final Cut 7 wasn't getting updated, and we all know what happened next.
That Apple scrapped a 10 year old, legacy design foundation that wasn't aimed for one that is primarily aimed at the next 10 years.... Yeah probably.
My guess is the new Mac Pro is a Mac Mini with better specs.
That is a poor guess. The size and power constraints for the next 10 years haven't really changed all that much so a "Mac mini" centered view would not be forward looking.
Mid range GPU cards are now hotter on average then they were 10 years ago. Not lower.
CPU's haven't really changed much either due to the 'core count' chase. The types of cores x86 versus GPGPUS/Vector may change over the next 10 years in workstation space, but the number is extremely likely to continue to go up. Therefore an unlikely large change in TDP requirements.
Shorter perhaps by 2-3 inches but that is hardly "mini" design centric.
Loosing ODDs isn't either. If holding onto rectangular shape the ODDs aren't the primary drivers of size in the upper , power supply focused thermal zone. That space easily be purposed with no huge size reduction. It is similar to the not being held prisoner to backwards looking legacy devices. There is very little to diminishing small justification for two OOD bays though.
Neither is an embedded GPU as long as there are slots and options to add a 2nd or 3rd GPU (or GPGPU ) card. Apple made add "mini" PCI-e slot form factor capabilities (Thunderbolt ) but it is unlikely if stick with Xeon E5 class CPUs that all the slots will disappear.
This hardware change is also deeply different from Final Cut Pro because Intel provides design reference boards. Apple doesn't have to re-implement the core structural design foundations from the ground up by themselves. The updates stopped being distributed to users while Apple rebuilt FCP from the ground up. That is fundalmentally different from work stopping.
There is absolutely nothing substantial in the rumor/news sphere that indicates that Apple was actually working on anything during the entire delay. In fact it is far more likely that that just stopped working on it altogether if the delay goes further than March of this year.
There will be a much better Mac Mini in 2013 and 2014. That doesn't say anything about the Mac Pro level workload space though. It does for the users whose workload does not now demand a Mac Pro level of performance. Most of those folks are going to move to mini's anyway if there is a new Mac Pro or not.
A "Mac mini Pro" would be just as unnecessarily cannibalistic of the iMac line up as a "xMac; Mac Pro half portioned" would be. Neither one is very likely to be released. There is no significant growth gap there at all.