I don't think it will be the last one, because Sony is in a position to make FF cameras more affordable than ever. Which means they will be able to reach out to a much larger public than before, even a potentially larger market than the other camera makers of FF cameras are targeting. Certainly much larger than the niche market for professionals.
Maybe, but you are assuming that a lot of amateurs would prefer a FF camera if they could just afford it, but that is old school thinking from those that used 35mm film DSLRs.
Not really, I'm hardly old school myself.

FF offers undeniable benefits, both in terms of noise performance, field of view, DOF control and resolution for a given lens. The overall balance sheet of all factors at play, may look different compared to the past, but there are still quite a few good reasons to choose FF at a given point on the technological timescale.
The trouble with FF cameras is the bulky camera
See my earlier post, Sony is in the position to make the cameras much smaller. Say the size of trhe A77.
and large heavy and expense lenses.
It can be heavy and it can be expensive. But that's a choice. Some would be happy with one or 2 lenses anyway, just like the majority of DSLR users as of now. Some would be delighted to use their old glass or some sharp but inexpensive lenses from Ebay. There's quite of few razor sharp but cheap Minolta lenses out there. They have their downsides, but I'm sure many would still be more than happy to use their strengths on an affordable FF body.
The main appeal for FF has been high ISO image quality and higher resolution, but that advantage is fading away as APS-C improves.
I disagree here. As APS-C improves, so do the expectations of the average consumer. And FF benefits accordingly from the technological advances. It's always easier to achieve a certain resolution with a FF camera, even more so as diffraction influences become more apparent at pixel level with resolutions going up.
The trend is for smaller lighter systems
That trend will undoubtly be seen in the FF market too and Sony has a high card there.
and Sony realizes that with the success of their NEX cameras, that outsell their Alpha SLTs by a good margin.
Can you link me to the source of this? One that covers
worldwide sales of both systems, rather than some retailer hot sellers lists.
Eventually most amateurs will be shooting with APS-C and probably even smaller sensor cameras. FF cameras are a hold-over from the film days and those days are numbered. The fact that Sony is so vague about the future of their full frame camera plans indicates they plan to phase them out quietly in favor of cameras that give them attention, play to their strengths and and make them money. I don't see how FF cameras fit into this scenario, regardless how low the price of their FF camera body.
With their strengths being weight, price and size, they can extend the life of FF quite a bit, especially if the existing benefits of FF that I mentioned before somehow turn out much less relevant and people will start weighing size, weight and price more often and more heavily. I have no doubt they see their high cards and value them accordingly. Especially since the production and design costs involved for a FF design, decreased quite a bit with the SLT design.