I've been keeping an eye on this thread and from my previous experience with the nightlies here's what I think:
1) Saying that modders help up the development process by keeping their mods updated and reporting nightly bugs is largely wishful thinking. Modders are not playtesters, so trying to use them as such will merely frustrate both developers and modders.
2) It is also irrealistic to expect that most modders keep up with the changes introduced by the nightlies. Again, modders shouldn't be expected to have the same zeal or availability of developers, since they will usually quickly move to their other gaming interests after they've finished their projects.
3) Most, if not nearly all currently existing mods will become unplayable on the nightlies until 2.0 gets released, and a lot will never be updated afterwards. A modder can drop by and update once in a while but you really need a lot of free time to be constantly updating a mod to be compatible with the latest nightly.
4) When OpenXcom 1.0 was released I remember a video review where the journalist said something that surprised me and it was like: "there's a ton of mods for this game now. I guess everyone was holding to their mods until the game got released". I now strongly suspect the same will happen when 2.0 gets released because of all the reasons above.
Personally, after my experiences in the past days, I'm going to pick a nightly that is "stable" and I'll stick with it while developing my current mod project. It's simply not productive for me to be constantly interrupted from creating new stuff because of the need to fix things that were working perfectly until the latest nightly got released. And if a player wants to use my mods with the latest nightly, well he/she will need to wait until 2.0 or I post an update.
Meanwhile, if playtesting is really needed, I'd suggest at some point to place a call on the forums and elsewhere for playtesters among the players. People whose sole responsability is to keep track of the nightlies and check the vanilla game (not the mods) for bugs. I'm sure a few people would volunteer to help.
Developers do their thing their way, modders and playtesters the same. And hopefully we all meet again at the end of the road.