Before Adobe can open Lightroom to third-party development plugins/modules, I think it's important they first stabilize their base. As can be seen by the LR2 beta, the Develop module is still very much in flux. With the changes being made, the addition of localized corrections (something which, I imagine, required significant changes to the 1.' base to implement), I think it's no stretch to say that the Develop module is the component of LR still most up-in-the-air, and, as such, probably the last that will be opened to third-parties.
Were Adobe to open that part of the the application to third-parties now, they might later find themselves backed into a corner where they'd have to choose whether to preserve compatibility with third-party addons, or make significant changes to the base to implement important new features, such as localized corrections, breaking third-party addons in the process.
I think it's much easier to support plugins for an app like Photoshop, in that it edits the pixels. But with Lightroom, the team needs to consider how best to handle third-party addons making non-destructive changes, and that, I think, adds a great deal of complication ...
Thems ma thoughts on it, anyway.
That said, I'd love to see a Viveza plugin for LR, and a Noise Ninja plugin as well. I'm going to keep my fingers crossed for LR 2.5 with Develop plugin support, or maybe 3.'. It might not be something we see until even further down the line, though ... Of course, Aperture supporting the plugins might apply additional pressure on Adobe to do the same, but then again ... Aperture serves only a very small percentage of the possible user base. Adobe only needs to compete with Aperture on the Mac; they have the Windows base pretty much to themselves.
