To me, a natural first Long Rest should be after the Dank Crypt.
That's exactly where I do my first long rest and get the go to hell scene. The problem is the mirror image scene can easily be missed if you:
- speak to Zorru > triggers Astarion cutscene
- speak to Sazza > triggers Shadowheart cutscene
- trigger Gale's reveal in some way (I still have no clue what triggers it, I miss it most of the time so I could be wrong about this one)
- speak to Nettie > triggers Raphael's cutscene
- find the dead boar/find Edowin (not sure exactly what's the trigger, but when I go beyond the underground passage I usually miss the mirror image scene, so I rest before I go there...)
Most players will probably trigger the first three or four cutscenes on the same day (and very likely also the fourth), which means that they will never see the first two (possibly three).
End of day cutscenes should be queued, they shouldn't override one another. I also don't see why Astarion's and Shadowheart's cutscenes can't be available at the same time once you trigger them. Why should one override the other? There's no reason why I shouldn't be able to speak to both on the same night. And if some cutscenes do need to take precedence (e.g. tadpole sickness cutscene) the others should just be postponed to the next long rest. But since, as things stand, even the queue could get too long, it would be best to have some of these cutscenes happen along the way, preferably during short rests.
