Well if Void and Celestial is what gets Infernal, I feel Void and Infernal may just get you back Celestial?
Yeah. Given that, I think I'll wait and see the results of earth+celestial first. Thinking about it too, we know moss gives ??? A, which, I'm going to guess is life, and we know
??? A is a basic essence. So that means it must be made via some combination of 2 core essences? If I'm understanding the mechanics right that is. Given that, earth+celestial doesn't seem too far fetched. Although ??? B (probably stone) doesn't seem like a weird of it either. Although that might be Fire+earth, if I had to guess. Edit: Just realized that I guess ?A might not be basic. Maybe?
The question now is: Should i do it? i legitimately want others' opinion. Should i switch one of my affinities to Infernal, or just keep the pseudo-affinity for it, by having an affinity for both of it's components?
This is certainly going to be a question for you to decide :P, but, for my own input, it does seem like infernal is what you were going for? Right now, we don't know what affinities do fully. If they are only useful for harvesting, you might be better off sticking with void and celestial in the short term, or at least not hurt by it. If they are useful for crafting it feels like you'll probably want infernal to make your undead zone? And later on if you want to harvest a bunch of infernal essence, you probably want to be infernal anyway...
But honestly I wouldn't base my decision on any of that, if I was you, I'd just take it because it's a interesting and special event.
The only issue is that afaik, you're the only celestial (well... Horizon is too but he's not posting every turn) and we have so much void, mechanically it might make sense for you to keep celestial, but, and this would be your taste so I can't tell for sure, but I feel like void+infernal might make more sense thematically. That's not a big deal at all though. We might not need celestial much, and even if we do, we can certainly use fate for it.