I bought C2 license 3 days after Ashley wrote the blog post about the future of Construct and C3. That was almost 2 years ago. Had I hesitated and waited it would've been a long wait for new version and limiting myself with the free version restrictions - in fact, we still don't have any clue when C3 might be released. Might be a month, might as well be another year.. or even more in the worst case. I wouldn't count on Scirra announcing an ETA for C3 many months ahead, as it wouldn't be a good business move on their part.
There's always something newer and better in the horizon, whether it comes to computers, phones or software. You just have to take the plunge at some point or you'll be waiting forever. I'm sure there will be a good upgrade plan/price point for C2 owners when C3 is finally released, I wouldn't worry too much about it. C2 is an affordable and plenty capable tool as it is, my advice is to just go for it and start making games now. As someone stated, the main limitation for most users is their own skill level, not the editor itself.