I'll venture a guess that the parts that are currently on the market (from multiple vendors, aFe, sxthelement, etc.) will be the last you see developed, specifically for the reason that the Elantra GT N-Line will disappear for 2021. Meaning the cars they can make compatible parts for are the following:
2018 Elantra GT Sport
2019 Elantra GT N-Line
2020 Elantra GT N-Line
That's three years of a car Hyundai neither made, nor sold, a ton of. There may be a few parts that are cross-compatible with all cars using Hyundai's 1.6t Gamma GDI (G4F4J) engined cars, so a few little bits that fit the Veloster R-Spec/Turbo/Turbo Ultimate of various years may fit our cars, but that's only if it isn't dependent on engine bay fit.
I would suggest that if you're looking for performance parts, now is the time. I predict production for many of them disappearing at the end of 2021, once 2020 buyers have had a chance to soup some things up.