Okay so I had this idea: How about we use the Rogue? Hear me out... Instead of Sneak Attack, you get some sort of 'Strategic Dice' or something and an 'Expose Weakness' feature to use them. Basically when you hit you get to grant the next ally to attack a bonus to their damage equal to your Strategic Dice. Let's say you start low with 1D8 at level 1...
But you can also trade each individual dice for a different effect! Trade that extra damage for temp HP instead, trade it for a bonus to accuracy, trade it for a bonus to saves, that sort of thing. As you gain more dice you can keep SOME of them for the damage bonus and SOME for the other effect. Once you gto 3D8 you could grant an ally 2D8 of temp HP and an extra 1D8 or damage, or vice versa. Some effect would need more of these dice than others. Temp HP is just one dice, but to grant advantage you need two of them. Those effect would work with Spells that have attack rolls to, not just weapons.
You could also trade your entire acton for Commander Strike and allow someone to make an attack with their reaction.
And the subclass could offer other uses of those dice or your entire action.
And of course you'd get replacement for the other class features of the Rogue.
The Rogue is interesting in that it's basically the only purely at-will frame and it has a lot of bell and whistles to hang interesting features on.