Don't know if this counts as a challenge considering how easy it was, but a submission for Non-Paladin no altar conversion: Dwarf Rogue of Dracul (+PM).
http://imgur.com/a/oia2wAvoided prepping Dracul to prevent bloodless horatio screwing me over, so I scummed for his altar only. Prepped draining blade and nabbed vampiric blade and one shot of Blood Hunger from Dracul for maximum lifesteal abuse, and fortunately Patches provided enough resistances early on to compensate for the incredibly late Pactmaker find. Stomped Horatio flat without any resist piercing options (forgot about the long rant too until he had >1000 health), and had well over half of my total bloodpools and blackspace remaining, so with a lucky tower shield or platemail find alongside something like bysseps (maybe even halpmeh since I was drowning in piety) Dracul-only rogue is entirely doable.
As for more intensive challenges, I have a few different ideas that I was considering if anyone wants to provide input on what to do/how to do it:
Purist Berserker - Currently my top contender for the next class to win purist VGT, held back only by an inexplicable abundance of goos on all of my runs. Gotten to tower 8-9 pretty consistently with the right start and Horatio to 3000 once.
Purist Bloodmage - Theoretically very powerful, but the complete lack of resistances at the start make it very RNG dependent, especially since taking Taurog gear on top of a max mana penalty puts serious stress on your ability for fireballs for goos and the like. Have had middling success with various taurog or gg/jj+pm starts.
Purist Transmuter - Above-average damage with Human and situational power spikes for tough targets. Honestly, I feel like if Tinker can do purist VGT then pretty much every normal class should be able to do the same, and Transmuter feels better suited than average for what purist runs require.
Purist Gorgon - I've done this more as a joke than anything else, but free 25% phys resist alongside poison strike and deathgaze doesn't look all that bad. Shame about the damage though.
Hoarder Thief - Extra boosters and stabber should make up for the loss of damage from being a human, and more potions/shops are always nice.
Hoarder Assassin - Damage boost from poisoning, free pseudo-first strike that doesn't take up inventory.
It's funny to think that these challenges once considered impossible outside of very strict class choices have now been conquered by a wide variety of classes and builds, and even more so that we still likely haven't tried all the permutations possible.