I don't think there is alot to "hone" or "balance" with more metals for example.
?? Sure there are. There's a
ton of stuff to balance!
Too many things near steel in power for example, even if individually reasonable = Much less of a need to care about your embark location = less challenge, less variety, fewer relevant strategies as alternatives to a simple well armed military, etc. etc.
"Provides an alternative when neither cassiterite nor flux stone are available on the map" is precisely
WHY it requires balancing... More alternatives are easier and blander and thus need to be balanced... For example, by carefully tweaking mineral amounts to offset it, or maybe making them not so similar in strength, or changing relative effort of smithing or mining, etc. etc.
Same goes for boiled leather, for example. Having renewable equivalents near effectiveness of, say, copper, waters down the game and requires appropriate balancing to make reasonable drawbacks so it's still actually interesting and some sort of a choice or sacrifice. It could totally work, but would probably need to require you to gather actual water and fuel and chemicals or something to make it sufficiently balanced, and the ratios of all the efforts and resources would need lots of testing.
More types of glazes isn't a balancing issue by itself right now, but that's only because large rock pots happen to be unbalanced/brokenly easy already. If those weren't overly easy and abundant and superior in every way, then glaze would actually matter for liquid sealing, and adding more glaze alternatives would need to be appropriately balanced. Ignoring that now simply means that if/when rock pots are balanced, you'll lead to imbalanced glazes waiting for you down the line since you didn't address it originally, etc.
Everything and it's brother being flux means that flux doesn't matter as much anymore, as it becomes closer to being just a given. Granted, borax wouldn't be a big deal, since it is sedimentary and thus not a big change. (although I do think it isn't actually more realistic). But that's still something you need to stop and consider, and if it were something more like marble that increased ease of flux access, it would require lots of balancing.
I'm not saying any of these things wouldn't be fun. I'm just saying its a job more efficiently left to modders, moreso than Toady. Unless there's a pressing need in the game for something, which I don't think there is for any of these things. At the very least not in alpha development.