Nicole's future prospects in the Stellar reaction meta are shaky at best.
I've seen a lot of speculation that Nicole will be "OP" or "irreplaceable" for Stellar reaction teams, mainly based on leaks that these teams will have high DPS contribution from off-fielders and the fact that Nicole can buff them. I don't think I quite agree with this premise.
Some numbers to demonstrate what I mean:
Assume an on-field DPS and an off-field DPS(es) both have 2,500 ATK before Nicole buff (which is a reasonable baseline since Stellar reaction characters will likely be on ATK goblets since they have their own DMG bonus type similar to Lunar DPSes and don't benefit from traditional DMG% from Goblet mainstat, or Nicole's set)
If the team DPS is an even 50/50 split between on-field and the off-fielders, Nicole on Skyward Atlas provides about a 29% team damage increase from her ATK buff.
If the damage split is 80/20 in favor of the on-field DPS, the total team DPS increase is about 32% from her ATK buff.
You can at most say her value doesn't drop (much) compared to other characters like Bennett, who buff only the on-fielder.
But why does this all matter, as long as she's better than Bennett in these teams? Because historically, a support is expected to provide more than a ~30% damage increase when you slot them into an existing 3-character team. Being better than Bennett for a team does not equate to being good.
And keep in mind 30% is assuming best case scenario where either "Reaction" Stellar damage scales off ATK (unlikely, considering Reaction Lunar-charged/Crystallize), or does little to no damage compared to "Direct" Stellar damage i.e., from talents that do scale off ATK
I think the value of Nicole in Snezhnaya is highly contingent on whether Hoyo plans to sell us 3-character cores (Flins and Nefer), or 4-character teams (Zibai). Considering Zibai is the more recent design and Hoyoverse has only gotten greedier with time, I'm more willing to bet on the latter where 3 limited 5*s + a new 4-star (ideally C6) will be the standard.