Hmm... On thinking about it the Battlemaster is
really missing one needed aspect of the Warlord, which is to yell at someone and tell them to stop lying down on the job and bring them from 0hp to back onto their feet. (The Banneret can actually do this part but has to wait so long for anything else).
But more warlord can be integrated as options into both fighter and battlemaster without substantial changes.
For the fighter (and paladin) I'd add:
Fighting Style: Teamwork: The fighter can use their attacks to distract enemies near them, creating openings for their allies. Instead of attacking this fighter may spend an attack as a set-up on an adjacent enemy. One other ally adjacent to that enemy may then use their reaction to make an attack.
Battlemaster Maneuvers:
- The Battlemaster needs more maneuvers anyway; the obvious design flaw in the class is that at seventh, tenth, and 15th level you are picking maneuvers which did not, for you, make the grade at third level.
- Maneuver: Stop lying down on the job! (Normally with more profanity). When you have an ally with 0hp who you can see and can hear you you may spend a superiority die as a bonus action. The ally regains that many hit points [or even just 1hp]
- Maneuver: Duck! When an ally you can see and who can hear you is hit you may spend your reaction to add the roll of your superiority dice to their AC. If the attack now misses the next attack against the foe has advantage.
I think that combination of fighting for others as a combat style and battlefield awareness and changing would be what it would take for me to feel that we had something that actually felt like a warlord.
Edited a full action to one attack for one attack in teamwork. It still only gives rogues an extra one sneak attack.