In just over two months we've gone from 0.8 to 0.89, as you can see here - so, assuming we keep up the same rate of release, some time in March we should arrive at 1.0. However, we still have a lot of documentation to do, so I'm guessing it might take a little longer.
0.89 is approaching a good level of stability. Why don't you try it out and post your feedback here? What is lacking most, and what is the biggest preventer of you making your big game? Feedback like yours is what we need to drive Construct to be what you want it to be...