OP – same for me, the thought of riding flats (on anything that is technical, fast or jumpy) scares the c**p out of me. I ride DH on Mallets, and they are fine – when you need to bail, you bail. I’d run SPD’s again if I could find a flatter pedal then the current Shimano ones, in particular as you can really slacken off the cleat tension – making it easier to bail. Lots of DH racers ride clipped in as do a lot of 4X and BMX racers – seems to work OK for them.
Final thought, I did try flats for a few weeks and ended up with more injuries, scrapes, near misses than clipped in – I can’t afford any kind of injury that would keep me off work, so clipped in it is.
It is personal choice, no harm in trying both, not worth risking things if you don’t have to