As well as it's doing in playtests, I still think the Commander would benefit from subclasses. Commander seems only to cover a portion of the "fantasy Commander theme" space available. So one reason to add subclasses is to diversify the types of incarnations available, but also to actualize some tropes which are struggling (like the leader spearheading melee troops). To be clear, I'm asking for solutions more than offering them! :-)
One pattern I've seen in the feedback is that melee Commanders get caught in an action bind. They want to Strike, do a Tactic, & Raise A Shield (which IMO they kinda need to do!) And since melee often involves more movement, they're left choosing between attacking as a mediocre martial or issuing their weakest (1-action) Tactics when ideally they'd contribute in both ways most rounds.
Meanwhile throwers seem to thrive while archers work fairly well (albeit closer than perhaps they prefer). Except that requires Dex, which struggles vs. having Str for one's heavy armor, Int as a Commander, and Con/Wis of course. Oy.
Spitballing:
One subclass which better integrates their melee Strikes (or movement) w/ their Tactics.
Another for archers (like one might imagine leading Elf squads), that works at longer ranges/in wider areas that sacrifices heavy armor & maybe Shield Block too.
And the last for skirmishers/throwers, though I'm unsure what they might need.
Unsure what else might suit a fantasy setting, but using the Rogue Rackets as a template we could also add one more magic/spell minded, helping casters more than now at least. And then maybe one that leans into their Int more (w/o participating directly unless pressed), perhaps with an action (with RK?) that adds Int to another's Strike damage (much like the Thief is unique in adding Dex to their damage).
And unlike Feats & Tactics (which I'd think an MC would require access to), one wouldn't need to worry about other (arguably more dynamic) classes poaching and becoming better iconic leaders than actual Commanders.