"A Sigil (rhymes with giggle) is someone from the City of Doors,"
sigil/vigil is a closer rhyme than sigil/giggle.
"While a Sigilite/ian might be new in Tristram, he's from mechanical city connected to every plane of existence."
I'm not sure what a citizen of Sigil is called, if it even has citizens, but common slang is "berk" or "cutter."
"Warrior: No spells from memory. No scrolls except Town Portal."
TP is quite apropos. Are Warriors supposed to be Godsmen?
"Visiting shrines is encouraged. Consider even Facinating, Ornate, or Sacred shrines as a low-level Warrior or Rogue. You'll be able to cast the spells you learned for the price."
I imagine Sensates would especially like shrines. New experiences are always worth the price.
Over all, my Planescape lore is too rusty to suggest much... but there is a hell of a lot of lore to be had, to the point where this variant could become arbitrarily complicated. But simplicity is easier to play. I will say that I don't quite yet see the Planescape archetypes you've crafted, but that could be because I haven't played PS:T in at least a year.
This variant's got me wanting to play Torment... *mouse hand twitches*