granting attacks
granting movement
forced movement
granting bonuses to hit / AC / save
inspirational healing
granting temp hps
what else?
bonuses to damage
ending conditions
condition immunities
granting re-rolls (attacks or saves)
forcing re-rolls (enemies)
marking (just marking, or marking on behalf of an ally - a related thing would be granting a conditional attack, like an OA)
and
There was a few ways to recharge encounter powers, but i don't know if that really translates to 5e.
Warlord's Recovery and the paragon path utility Bolt of Genius as actions, No Gambit is Wasted as a reaction, and some others. In 5e it'd have to be something like 'gain one specific benefit of a Short Rest, within such-and-such parameters...' nothing like that exists that I'm aware of, so that's one, I suppose.
And guileful switch, but that probably causes too much confusion to be worth it.
(Take all the confusion out of the game and what would you have? A 1st level Champion Fighter, maybe.) ;P Seriously, though, from Combat Leader to Stall Tactics to Guileful Switch, messing with Initiative was definitely a possibility.
...and I'm sure there are others if you want to comb through all the exception-based tricks 4e came up with for the class...
Now a lot of those aren't hard to come up with. You didn't mention an damage bonus, for instance, and even if there isn't a martial buff-an-ally's-damage mechanic out there, it's not like it's a novel or problematic mechanic. It's a simple bonus.
Maybe not everything, but enough of the stickier mechanics it'd take to design a full warlord class have been tackled that actually going through with it should certainly be possible, even with such limited resources as they seem to be struggling with...