New race starting points/maps.

I can't be the only one who thinks the idea of running through act 1-2 5,000 times is very enticing? I mean, essentially, once you master a route, you are just going to be going through the motions anyway. There isn't really anything there to challenge you outside of dealing with bad RNG.
Why not have some races start at different act points? Or even better, make use of the map system you have and instead of even doing the same format as the regular game, just have it be a bunch of connections randomized zones, with randomized monsters. Talk about the ultimate RNG race.
You could even go further and take away some RNG elements and give people access to a set amount of skill points and gear at the start of a race, they must use this gear and the passives to build their starting character and then go forward through a bunch of increasingly difficult maps. Those maps could even have map mods applied to them.

Races with different starting points (act, difficulty, character level etc) have been suggested before, and would be strong skill testers, as well as a refreshing change.

Fixed starting gear/gems was another idea i suggested a long time ago in cb- combine that with static monster spawns and fixed, revealed area seeds and youve got the ultimate pure skill race.

The randomized area with map mods race is a great idea. Something like 30 Maelstrom of Chaos style consecutive zones, starting at area level 1 and increasing 1 level with each zone transition gate passed. Boss at the end of each area guarding the gate, which doesnt open until the boss is slain. Start with a single map mod from zone 5 onward, adding another mod every 5 gates (capping at 6 mods for the final level 30 zone). Map types and monster types would be standardized on a per-zone basis (either for each race or for the season), but the map seeds and monster spawns would be random as usual. This would translate to longer races (50+ zones) pretty easily as well.