My answer is going to be based on speculation of what I've seen so far as I am hardly one of the many users who are in the loop for such technological developments in Colorado. I'm sure someone else will be able to chime in with information that they do know at some point. The State DTR System likely won't go through a Phase II upgrade until they have secured some type of major funding for upgrading 200+ sites for all of Colorado. Given that it took a bit for the state to secure the funding needed to do software upgrades (part of the reason why Weld and Adams opted for FRCC), it might not happen for a few years as they like to make changes all at once.
Even with a Phase II upgrade, each agency would then need to coordinate a massive department wide replacement of radios to support true Phase II operations. A Phase II system will remain Phase I as long as a single radio affiliates to a talkgroup that cannot do Phase II. There is a pretty significant amount of radios in Colorado that are Phase I only, purchased prior to the finalization of the Phase II protocol (eg. Motorola XTS series). I don't see a lot of the agencies making a switch to Phase II the day DTRS is upgraded to Phase II due to costs to the individual agencies.
As for the other agencies that already have Phase II capable systems, it really depends on the agency. I have a feeling that Denver, Arvada, and Westminster are all candidates for being the first agency to switch to Phase II since they all purchased (or are currently purchasing) new P25 radios to replace their old system and don't really seem to have anything big holding them back from doing so (except for being the first agency to work out the bugs). West Metro and Lakewood may also have the ability to go Phase II since they are also sort of new to the P25 game. Other than that, I don't think FRCC will see Phase II usage for a couple of years as they mostly recycled their DTRS radios onto FRCC.