You need to choose your topic by yourself really. That is the name of the game. Of course you are biased with your opinion but that is ok!
I think there are topics on that list (and beyond it) you feel more comfortable with. Why do you ask people for something when you probably know what is the easiest for you?
i just want to get some inspiration and avoid my own tunnel vision really. normally i would just talk to friends for this kinda "brainstorming" thing, but sadly they are not as interested in those topics so it doesnt really make sense.
also.. it's not about what's easiest, it is about whats interesting and fulfilling.
ps.: i also wanted to find out if there are some fields in crpyo/btc that need research to be done, sort of helping out on that.