Was going to comment on the recent slings/thieves FR (2928575), but it was already closed. I've always thought that the aptitudes are wrong, for one; thieves should start with higher stealth than assassins for logic reasons; also, avoiding combat until the temple is much more crucial for the thief than the assassin, due to lack of a blowgun. The thief god is a good idea, if monolithic: it might be interesting to have other options in chargen, as an either/or option (starting with a deity or with item choices). Anyway, here are some possible starting gear/aptitudes for the class:
lvl 1 evocations and a rod of discovery (makes sense from a flavour perspective, but might be overpowered)
Gold...also for flavour, and doesn't help on the first three levels at all. However, it would make the early weakness more compelling (shops/troves)
Blowgun with some of the new needles. Kind of makes the class too similar to assassin, but might make for interesting play, i.e., using needles of confusion to get away from Sigmund. Alternatively, starts with some of the new darts (reaping might be an interesting choice)
Starts out with some potions/scrolls pre-identified. Alternatively, starts with escape items: potions of invisibility, scrolls of fog, teleportation, fear, etc
Put the crossbows exp into stealth/dodging/etc. It doesn't make sense to have skill points invested in it now that hand crossbows are gone.
Starts with gauntlets of legerdemain, which grants a stealing effect when one is within one square of an enemy (this would be a non-god way of addressing theft in the game, incidentally). Could be ultra-rare in the main dungeon. In theory, it would have a small passive chance of theft when being attacked, a larger chance when attacking, and the largest chance when adjacent to unaware/distracted monsters. This could lead to interesting situations when Terence has a wand of draining, for instance. Could be hard to balance, but solves another (sort of) issue: there aren't any normal gloves which compete with artifacts.