I'm probably going to go full S&S, but with some D&D races instead of just humans. Something kinda similar to Iron Heroes in feel, where 90% of players and NPC bad guys will be fighters.
Some current ideas:
Limited to level 10, as previously noted. I might make Level 1 = Level 2 or 3 of basic D&D, though. I want characters to be competent right off the bat, though still not invulnerable. Lots of different professions to differentiate them. For example, archers will get +1 to hit with ranged weapons, while templars will get +2 damage to all undead.
Mages will also be a bit more powerful, starting with 2 level 1 spells and 1 level 2 spell, and working up from there. I will likely require a minimum Intelligence of at least 13 to be a mage, and maybe higher. I want them to be rare. Spells will focus more on wards, summoning and divination, and less on fireballs. I might also give them some kind of fairly powerful familiar that will require blood, murders, or lots and lots of gold, or their spellcasting will be severely limited. Basically, a simplified pact system of some type. I will definitely avoid anything too complicated, like some of the systems introduced for 3e.
Still have lots of ideas kicking around, and nothing is set in stone right now.