I don't know if that will be the case...
The discounts with VI on sites like GMG were fairly immediate. Anecdotally, I think preorder prices for games across storefronts generally don't change.
In other words, my guess is what we see is what we'll get in terms of preorder pricing.
No, at least back in 2016, the real discounts on Civ 6 were time-limited and ran for a few weeks in the run up to launch. Not saying this will happened again, but it definitely was not at that price on GMG for the whole preorder period.