Since January Wizards have started a series of regular articles for DnD 5e. One of them is Unearth Arcana which presents rules idea and variants. This week's article is on mass combat!
Update: Looks like Mearls and his team opted for a miniature based wargame for mass combat. Each figure represents 10 combatants except for solo characters. The stats for each figure is as per their stat block or character sheet. The combat round is structured differently, but the attack procedure is the same as regular combat.
It looks like their reasoning is that each figure or "stand" represents 10 combatant and each mass combat round is 1 minute or 10 normal six second rounds. So rather than some up with a alternative stats, they just bumped up the time by the same amount as the figures. Characters (NPCs, PCs) get a bit of a boost as they fight 10 combatant just like a single opponent. However a PC attempting to got at it alone would be considered isolated and suffer double damage on a successful attack Given the multitude of "stands" involved that is a lot of hit to absorb even for 5e with its increased hit points.
I think this could work well. I will dig in deeper and report on what I find.