Come on, I can't be the only one that's been thinking of this!

The trouble is, which Mare-Do-Well would they meet? The mage, the flier or the psychic?

In my (rather poor) story I had them met both, with Mare-Do-Well being different in each counter so they were baffled...for about two seconds because they mostly interacted with Daring Do.

...yeah, it was needlessly complicated fic now that I think about it

This dos gave me the idea of making another version about it...

2592012 Or some hybrid who has all the abilities that Mare-Do-Well seemed to have?

It sounds like the whole Teen Titans versus Red X thing.
"But wait, I WAS RED X," said Robin, "So WHO could be RED X NOW?!"
...
Besides, it seems Mare-Do-Well wouldn't appear in the comics, so the Power Ponies would somehow have to come to Equestria. That would be awkward.
...
Hmm, Princess Cadance or Princess Luna as the new Mare-Do-Well? Am I the only one thinking this?

What if Mare-Do-Well was actually an enchanted outfit that more or less possesses the pony wearing it and makes them fight crime (maybe giving them a power boost as well?). So an earth pony would get the boosted speed, a Pegasus would get enhanced flying, and a unicorn gets boosted magic?

Maybe something like Spider Mans black suit? I heard that in the origional comics the black suit wasn't evil by default, it more or less was a straight up symbiot that enhanced Spider Mans abilities. It was only later that it became Venom.

So Mare Do Well could be a sort of symbiot, enchanted outfit, or maybe a shadow demon nightmare thing that gives enhanced powers to whoever wears it? Like, it was dreamed up by a Luna-expy who didn't have powers of her own but could create more or less anything using dream magic. So she dreams up an outfit that gives powers to whoever wears it.

She wears the outfit at first, and has a run as an awesome superhero before becoming more comfortable with her dream powers and taking on a new identity. The outfit is passed on to another who takes on the mantle of Mare-Do-Well, and so on.

It could then wind up as a semi-sapient suit that locates ponies in need and 'empowers' them to fight the good fight, only to leave them once they have finished their own personal story. So that the city always has a Mare-Do-Well, but its almost always a different pony who's fighting a different disaster, who can then retire from crime fighting to live a normal life afterwards.

It might even occasionally wind up on a villain or criminal who then abuses the suits power for their own gain, but by the end of the issue, they find that they could have had a much easier time using it for good or to solve a greater problem. Or the Power Ponies have to beat up the Neigh-Do-Well to rescue the suit.

2591812 actually, I've been thinking about a sort of alternate "Mare-do-well" that was a pony that could switch between the three races, but have enhanced abilities.
Earth pony = super strength
Pegasus = erm...*tries to think of a superpower that pegasi can't already do*
Unicorn = enhanced magical ability