I think the resistance you are sensing comes from the fact that the Stack Exchange question you linked has a strong undertone of something like “It’s been a decade, so why is there nothing to show?” That is also why I mentioned that a better way to look at the problem is from the perspective of what’s left to do (or as you say, what needs to be solved). You’ll likely have a more positive interaction here on the HTM forums from that perspective.
Anyway, there is a lot of opportunity to improve HTM. A better way to handle repeating sequences is an obvious one (as discussed on the thread @jimmyw linked to). I believe the solution for that problem involves feedback from a pooling layer (which is the direction I am currently exploring in the Dad’s song project).
If you’re looking for a somewhat larger challenge there is the so-called “numerous fields” problem. This one will likely involve feedback from a pooling layer, voting, and hierarchy.
How to implement attention is another one. We had a nice discussion on that problem recently on this thread.