There are some really good ideas coming out of this thread. Here's a sample progression:
(But it's probably redundant to give the Warlord 2 dice pools! Maybe instead of superiority dice we could borrow a page from PF and introduce special abilities similar to teamwork feats.)
Warlord
The warlord is a martial class who focuses on battlefield tactics, helping his allies fight as a cohesive unit and increasing their staying power through inspiring words and a helping hand at just the right moment.
HD: d10
Skills: 2 of Acrobatics, Athletics, History, Intimidate, Medicine, Persuasion
Fighting styles: choose one of Defense, Defender, Duelist, (new style for commanders)
1: Fighting style, Formation Fighter: The warlord can use a bonus action to take the Help action for an adjacent ally.
(Note: overpowered? But consider all the things that regular fighters can use their bonus action on, typically an attack)
2: Inspiration (similar to bard dice)
3: Superiority dice and maneuvers
4. Push the Limits: an ally who uses an inspiration die can also spend a HD to recover HP as a bonus action, add the Warlord's Cha bonus to the roll.
5. Extra Attack
6. Battle inspiration (Valor Bard feature)
7. Hold the Line: When the Warlord uses the Help action, he can give advantage to 2 adjacent allies.
8. Larger superiority dice, more maneuvers.
etc...