I in fact AM a dev on Quark! So if I may give my two cents on your suggestions:
1 - I think its a lovely idea to have something like that. Maybe not Slime Balls, but something that kinda does that oxidization sort of process.
2 - I do love block variations. So sturdy stone for blackstone and deepslate could be fun to see.
3 - Though in previous versions there has been backports, I really wanna avoid doing them as much as possible. I don't think Quark should be that type of mod. It should be what community ideas really mesh well with vanilla, not just future vanilla ideas.
4 - While I could definitely see us doing something like that in limited amounts, I'm pretty sure we are trying to not have as many just large swaths of the block variations. A mod like what was seen during 1.16-1.19 with Consistency+ would be more fitting of that.
5 - I could see a feature like that being kinda fun! I'll see if people want to consider it.
6 - As previously stated, we do have a pre-end recipe for the iron rods.
All in all, these are some nice suggestions, and I'll definitely ask the rest of the team what we think of some of them