We know GM is developing diesels for the US. My question is how are these going to be released? Will they be launched just in new models and MCEs, or will they be made available for all models that can take them ASAP?

The reason I am asking this is that my ideal vehicle would be an SRX, and I am wondering the probability that GM would release a diesel version of it as the engine becomes available, especially since its future is in doubt. I want to be green as well as plan for the future (diesel engines can switch to biodiesel fuel with no problem, whereas a gasoline engine making a fuel switch needs modifications).

I can't answer this with any certainty - no inside info here, but...

I highly doubt they'd just suddenly offer it in any model they could possibly drop it into. Each model will require testing & such, plus production capacity is likely to not be able to handle a large number of models right away. Look at the new 6 speed auto - not immediately available in everything it could be in, but it is spreading.

In CA, I wouldn't hold your breath. Tier 2 Bin 5 is incredibly expensive to meet.

There will be no diesel SRX. Much less an SRX period in the not-to-distant future.