If that's the criteria, you've lost before firing your first bullet.
There's only a couple of 5e classes that had long-time fans of their up in arms - the Sorcerer and Ranger. That's not a terrible track record. Surely, you're not implying that WotC has suffered some drastic loss of game-design competence in the last few years? Or are you privy to some secret information, like Mike Mearls had a stroke and has been replace by an LMD?
You can't make everyone happy. Nothing can.
Right. And the first cohort we should remove from 'everyone' to get a potentially-please-able audience is:
Even if we ignore all the h4ters and obvious negative opinions
Yep, those guys.
, there is a sharp divide among the "fans" as to what and how to do it.
There's one vision of the Warlord: the 4e version, that all Warlord fans, by definition, were happy enough with. It's a model that 5e should have no trouble emulating, it will just have to add to it to fit the 5e paradigm.
Where warlord fans fall into sharp disagreements is in discussions like these where detractors keep asking for 'concessions' and demanding justifications for the class far in excess of what's ever been asked for with any other.
That individual fans come up with different things they'd be willing to part with - and some find one of those same things 'most-important' doesn't mean there's an unbridgeable gap among those fans. It just illustrates how varied and interesting the class was, and that all that breadth & interest needs to be realized in 5e.
Which is not a tall order. 4e was a more restrictive design environment than 5e. It'll be much easier than it was.
Warlord faces some serious issues it needs to sort out before a consensus can be reached: the first being its frakkin name (its amazing how many people, even self-professed warlord fans, hate the name "warlord")
It's the worst proposed name for an additional martial class beyond the fighter - except for all the others.
Seriously, the objection to the name is spurious nonsense. Spurious nonsense some warlord fans are willing to get behind if it means getting the class they want in all but name, and others are justifiably offended by.
Further, unlike all the other classes released so far, there isn't a non-4e version of the class to look at for a guide on how to mimic without the ADEU structure.
Yep, there's more freedom of design, there. Of course, AEDU /was/ used, loosely, as a framework for the Warlock (or you could say the 3.5 Warlock presaged AEDU), and it worked quite nicely. All casters now have at will (A) Cantrips, and of course, D&D has always had daily (D) spells, many of which have utility (U) beyond attacks. 5e even gives some casters a short-rest recharge of an otherwise daily spells, so the E is there in more than just the Warlock.
So, not an issue, really. Use a short-rest focused AEDU-ish framework, like the Warlock, or, y'know, show some design chops and come up with something unique that accomplishes the same goals in the context of 5e.
The only real challenge in creating the Warlord is in making it effective and versatile enough to stand in for a Cleric, Bard, or Druid (or, for a bravura warlord, Paladin, I suppose) without putting the party at a profound disadvantage. Simply porting the Warlord from 4e - strictly-limiting AEDU and role structures intact - would fall short.
Even further than that, there is still a large gulf on of agreement on what a warlord should be able to actually do.
The Warlord, Cleric, Bard, & (Sentinel) Druid were all leaders in 4e, and the Paladin was a strong secondary leader. In 5e, the Cleric, Bard, and Druid are all first-tier support classes, and do more than ever they did in 4e, besides. That's a clear target in necessary contributions, and nothing inhernet in the system stands in the way of it.
For another example, take support. This catch-all term generally means "can replace a cleric/druid/bard in a party" but its hard to say what the warlord is doing and how is he doing it nonmagically.
No, it's not hard to say. It's just that some people who already hate the warlord don't like what it's had to say on the subject.
That's why the warlord isn't for them, and, if I'm to get off my high horse and be pragmatic for a moment, why it was a 'good' that it was excluded from the PH. That makes it necessarily optional, so anyone who doesn't care for the narratives around martial support can just choose not to opt into the class for their campaigns.
There are some default narratives some folks just plain don't like. Vancian magic has probably repelled more potential D&Ders over the decades than will ever be exposed to a Warlord class, let alone repelled by it, but it remains, in somewhat bowdlerized (yet less restricted, even more versatile) form, none the less - and, with clear alternatives like the AEDU-ish Warlock available. Those who still can't stand it even have an optional spell-point rule in the DMG, too.
And, nothing really stops us from using mechanics, but rationalizing our own narrative that does work for us. And, nothing stops DMs from tweaking mechanics. Those that /did/ like classic Vancian, for instance, can't possibly find it difficult to just treat the three prepped casters as such, using slots as old-school daily spells. Heck, the game probably 'balances' a little better that way.