How about “Kaloopa Troopas”?

[Eric B]

When SMW was released, they changed so many things; one of them redesigning the Goomba from a two-part mushroom body, to a single walking head, and that it no longer squished with one jump; you now had to jump on it twice, to flip it over, and then to kick it away (Basically like the old Koopa Troopa, but not sliding on its own).
They afterward went back to the earlier form and defeat behavior, but in 3DW decided to bring the SMW form back as a separate character, the "Galoomba", side by side with the regular Goomba. Afterward, the name "Galoomba" was retconned back to SMW (especially on Mario Maker).

So on SMW, the same measure of changes had been done to the Koopa Troopa. They now walk on twos instead of fours, and now you have to jump on them once to kick them out of the shell, and then dispose of the naked character and the shell separately. This, like the new Goombas, felt so different from the original.
However (unlike the Goomba), in subsequent games, they kept the two legged design, though, I believe, restored the always in their shell behavior. The Galaxys were the only exception where they were four-legged again. In 3DW, they revived the pop out of their shell behavior, and so that once again is how all of them are.

I had never liked the SMW designs of either character, but was glad to see the Goombas split into two distinct characters. I think that the same should be done with the Koopas. If the SMW Goomba is really a "Galoomba", then the SMW Koopa is a "Kaloopa"! It's so obvious! Restore the original Koopa Troopa form where they walk on all fours and stay in their shell, turning upsidedown when stomped, and kicked away in one piece. The current upright version becomes a "Kalooopa troopa", and pops out of his shell when stomped.
You can have them together, for whatever new Mario series and Mario Maker game.

 

[Glowsquid]

The modern Koopa Troopa design in Super Mario Galaxy walks on all four so do they become an entirely different species when they decide to stand up

 

[Waluigi Time]

I think if there was going to be any retcon like this it would make more sense for the four-legged ones to be Shellcreepers and leave the Troopas as-is, after all they've been that way for over 30 years.

(Also I feel obligated to mention that the Galoomba situation wasn't really a retcon, they were always separate but the English translators didn't give them their own name until 3D World.)

 

[Eric B]

The modern Koopa Troopa design in Super Mario Galaxy walks on all four so do they become an entirely different species when they decide to stand up

Well, Galaxy was over a decade ago, and when they picked up the NSMB series and then 3DL/W, they went back to upright. So I would call those the "modern" designs. (Odyssey I forget; do they even have Koopas, outside of the 2D sections?)
But yes, my idea is that the upright ones (and which pop out of their shells) should be a separate species.

I think if there was going to be any retcon like this it would make more sense for the four-legged ones to be Shellcreepers and leave the Troopas as-is, after all they've been that way for over 30 years.

That would make some sense, though I'm looking at the original SMB as the model. (For one, shellcreepers were a little different and could not be hopped on without flipping them over first, and also got out of their shells to put them back on when going right side up. In that way, they're actually a bit more like the modern Koopas).
And they did not always pop out of their shells for the entire 32 years, plus, again the Galaxy design.
So it seemed better to consolidate the SMW characteristics as another character like they did for the goombas. And Koopa/Kaloopa is a nice parallel to Goomba/Galoomba.

(Also I feel obligated to mention that the Galoomba situation wasn't really a retcon, they were always separate but the English translators didn't give them their own name until 3D World.)

Galoombas started with SMW, where they were simply the "goombas" but with the new design and game dynamics.
Just looked it up and see they were used in one place in SMA4:SMB3:E-Reader, which otherwise used regular SMB3 goombas (though with the SMW-like 16 bit graphics), and this would be the first instance of it being a separate character, and undesignated (the game imported a lot of SMW items such as wigglers, and there's SMB2 Hoopsters ar well).