A real, proper warlord.
The only feasible idea of making it a sub-class that I saw so far was elfcusher's idea of trading attacks for bonus reactions.
Reactions being instant-bonuses to minimize the stuff that you need to keep track of, as well as making the warlord more actively involved and giving a different feel from the pre-buff spell classes.
Trading away attacks makes enough room for the abilities. And if you don't use your reaction, you can just hit stuff like normal.
A quick version.. (needs stuff like "only people you can see" and such).
3: Preemptive Action: You can trade 1 attack on your next turn to take an extra reaction now. More trades with multi-attack.
Tactical Adjustment: You can use a reaction to reroll any (enemy or ally) attack or skill check within 5'. Combines with protection style to reroll enemy attacks with disadvantage.
Poetry in Motion: You can spend a reaction to extend the range of another reactions, moving up to your speed to get into range. Does not provoke OA's.
7: Predict Failure: You can see failure comming, and let people know not to waste their resources. After a willing creature takes an action and you see the die rolls, you can spend an action surge to cancel that action, keeping their spell slot/resource. The creature can take another action. It cannot be the same one you just canceled.
10: Bolster Save: You can use your reaction to reroll any failed save within 5'. Including death save.
Greater Poety in Motion: If you use poetry in motion to move less than half your speed and would not have provoked an OA, you do not need to spend the second reaction.
15: Tactical Readiness: When you roll initiative and are not surprised. You can give Int creatures (min 1) either gain a bonus to imitative, penalty to initiative, or can move half their speed. You can use this after you see the rolls but before battle starts.
18: Perfect Plan: Once per short rest, when a creature within 5' that's not you makes an any attack, save (including death save), or check, you can use your reaction to make the d20 a 1 or 20. You must use this before they roll.
This could also work as a rogue sub-class, trading away future sneak attack dice for instant-bonuses. This has the advantage of being able to price different abilities, and works nicely with cunning action's extra movement.
2d6 to reroll an attack.
3d6 to allow movement.
4d6 to give 1d6 bonus to a save.
6d6 to give 1d6 penalty to a save.
ect...
*IMO, preventing 2d6 damage in as good as healing 2d6 daamge. Plus the healing and inspiring leader feats go with fighter's/rogues extra feat. So non-magical healing isn't needed.
*Rerolling attacks replaces granting attacks. Effectively the same, but with a lower max damage, works with firebolt, and is not crazy with eldritch blast. Most trades are good, since everyone but the fighter everyone get's a bonus to damage.