You can HP Castille and it's just fine. You still need to give it time to harden up and it won't be as white as it would be if you did CP and avoided gel. Other than that there's no difference.
I recently tried pure castile with 40% lye solution (nice big water discount).
I poured the just mixed, SMOKING HOT lye into the room temperature oils, and stick blended to trace. Only took a couple of minutes, and the soap was ready to cut the next day. It's less than a week old and it's already getting hard as a rock.
Not exactly hot process......more of a RTCP followed by an oven gel, but it's quick and the texture is gorgeous.