I feel like I've seen this show before, with other acquisitions of a generalized tech by very vertical entities. So I'm not getting really warm fuzzies about this. With apologies to Mark Harrison, who is an amazingly great person (I had the pleasure of getting his assistance with a user group meeting), and John Bacus (who is also wonderful, and gave a lovely presentation to our group), I'm just not buying the "nothing will change" line. I hope that I'm wrong, but consider - under what circumstances is SU helping Trimble's bottom line?
The "success metrics" for SU are determined by its owner. Google clearly sought to profit from SU in a pretty oblique fashion, although their mission for SU was kind of unclear to me (does this mean that they're going to kill off Earth, or some features of it, too?). Trimble, on the other hand, will definitely be looking more directly at the bottom line. Thus, we can assume that almost everyone that uses SU today, and isn't at least a potential Trimble client, is going to get leftovers. Unless, of course, that new developments overlap between Trimble clients and everyone else. And it could be that such overlap is very large, as we have little insight into what Trimble actually is seeking to get out of this. Or it could be the opposite, which is what I'd expect.
I expect that the PR efforts will be to keep users and plugin devs from bolting initially (because the devs seem to be part of the value equation for Trimble), and it'll be business as usual for a while. Perhaps even a long while. We might even see SU9 land in a form that's effectively the same as what a Google-owned SU would have been (as it must be pretty far down the road at this point).
But eventually I expect the hammer to drop. Trimble does (or doesn't) do something that's a deal-breaker with the community. And then the community either finds a new tool, or creates one.
Is it time for all the dev rock-stars to create CloneUp? I'd imagine that a Kickstarter campaign for that purpose would raise tankers of cash to do so. I already have my wallet out 
One thing to note that may inspire some positivity, from the Trimble press-release: "The deal is expected to close in the second quarter of 2012, and it would not be material to Trimble's 2012 earnings." Q1 GAAP earnings were in the $40mm range, so it'd appear that the transaction between Google and Trimble was mostly or entirely cashless. Might mean that the deal came with (user-friendly) strings. Let's hope so.
And lastly, I do need to acknowledge that both Mark and John are both stand-up guys, and as much as I tend to be a Cassandra, I cannot ignore my (contradictory) feeling that I find it very unlikely that they'd mislead us in any way. And that might render all of my fears moot.
This is entirely my own uninformed opinions, and should only be considered as pure speculation across the board.
