I haven't seen a way to get guarantees of upscaling operations under like 30 seconds (with Multi-AZ RDS) with well-supported RDS stuff (leaving out active-active setups with logical replication because that's a whole other can of worms).

If you know you're gonna be ok with that for a long time, go nuts. I'm just saying: think about it in advance!

The cost pain for spikes is also a thing - some of Aurora's billing models look potentially promising but I haven't used them in practice - though it's also somethings that's harder to avoid with alternatives. Distributed DBs aren't generally super friendly to dynamic scaling IME.