I think I will buy the core game and maybe one big expansion... Damn you FFG if you release a new Runebound very soon...
It can be very frustrating when that happens, unfortunately, there's not a lot you can do to predict whether it will happen or not. It's true that the expansions seem to have died out, but does that mean a new edition is on the way, or are they just going to let this one sit for a while? Only time can tell (and FFG, of course, but that's not really the sort of question they'll answer.)
If it's any consolation, FFG has not, in my experience, been known to release a new edition JUST for the sake of releasing a new edition. IF they release a new edition of something, it is because they have some ideas for how to significantly change and improve the game (at least in their own opinion.) They generally do a good job of addressing the flaws of the previous edition and making things all that much better.
By way of example, I have a friend who owns all three editions of Twilight Imperium. He does NOT own them all because he's a blind fanboy who purchases everything FGG publishes. Each time they made a new edition, he waited until he had a chance to see and play the new one, and even then he was skeptical about whether or not the new edition was "worth it" considering he already owned the last. Each time, after having seen the changes to the new edition, he agreed that those changes were significant enough to warrant upgrading.
By now, you may be wondering what my point is, exactly, so I'll get right to it: Runebound Second Edition doesn't really have any great flaws. The biggest complaint I know of is the downtime between player turns (particularly with 4+), and it seems to me that this flaw alone is probably not worth revamping the entire game engine. The changes required would probably be fairly extensive, and who knows what new issues would surface as a result? What I mean to say here is that, unlike other games such as Descent, Runebound doesn't have a lot of NEED for a new edition, and despite what some might say, I haven't known FFG to release a new edition if it wasn't needed.