I actually had an idea pretty similar to your "Infernal Torment". :p I was even gonna call it Inferno aswell!
I wanted to make it work with personal clears in mind, if I clear GR80, T1 on Inferno ticked (add some checkbox when selecting level difficulty or w/e) would be GR71, T2: GR 72,... so TX on Inferno would be equel to your highest GR clear. I'd just really love something like this since it'd make the campaign fun again. I wanted to clear it the other day since I rebirthed my original vanilla DH (and it's been a pretty long time since I last cleared it) and it's really no fun when you just 1 shot everything. :/
I really like your other ideas aswell, definitly the Artisan Leg gem one. The only thing I'm unsure about is having Kadala give legendaries only, on the other hand, yellow items are completly worthless now anyway.
Great job man!