You're saying 100+ MB/s won't be enough anymore? Why would that be the case?
SD cards also have the drawback of having pretty limited write cycles compared to any SSD.
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.