That is how every previous Nintendo back-compat implementation has worked.
GC on Wii
Wii on Wii U
Game Boy on Game Boy Color
Game Boy/Color on Game Boy Advance
Game Boy Advance on (New) Nintendo (3)DS
Nintendo DS on Nintendo DSi
Nintendo DS/i on Nintendo 3DS
Nintendo 3DS on New Nintendo 3DS
In every case, the system drops back to the earlier console’s hardware specifications. There are hybrid cross-gen games on some of the handhelds which offer improvements on the newer hardware, but up to this point, older games have never been updated to get the improvements of newer hardware. That doesn’t necessarily mean the same will hold, but I’d suggest you assume it will and be pleasantly surprised if they buck the trend.
That is how every previous Nintendo back-compat implementation has worked.
In every case, the system drops back to the earlier console’s hardware specifications. There are hybrid cross-gen games on some of the handhelds which offer improvements on the newer hardware, but up to this point, older games have never been updated to get the improvements of newer hardware. That doesn’t necessarily mean the same will hold, but I’d suggest you assume it will and be pleasantly surprised if they buck the trend.