You're saying 100+ MB/s won't be enough anymore? Why would that be the case?
Plus you're gonna be targeting a much wider userbase for the time being by not targeting SSDs.
So then yeah, sticking with a load screen _might_ be easiest. But if the tooling supports it, it might be even easier to just not worry about loading and having to make a loading screen, and let the engine handle that stuff for you. UE5 at least seems to be going in that direction.
SD cards also have the drawback of having pretty limited write cycles compared to any SSD.