But yeah, beta 4 will be filled with all kinds of sidequests, most of them being accessable just before it's about to end. It will also reveal more of the story and end in a point, where you'd actually want to see how it's going to go on, but there is really nothing I can do about it.
After that (for beta 5), there won't be any more sidequests to do because I've planned the game to go on like that; there is simply nothing that will make you receive some sidequest that wasn't doable earlier. But what will be good about it is that, beta 5 will cover a lot more story (and interesting storyline-related events!).
And finally after beta 5, I'll release the final product with another sidequest (or two) in it, but one is really a major one (totally, the longest sidequest introduced in the game)! It also covers interesting background information related to the storyline, which will reveal the "missing pieces" of the story in player's aspect.
And, that's the plan basically