I don't know. Despite my qualms with mechagnomes, they are somewhere in a development limbo between reskin race with extra options (a la dark iron, mag'har, etc.) and their own model like vulpera.
I don't know if they could've just been offered as a customization option to gnomes. Maybe, arguably- thinned down a little. Best would've probably been to 1. have ankoan instead of mechagnomes, or 2. Have them fully mechanized.
Ankoan use the night elf skeleton, but they are their own species (if you ignore the unplayable Jinyu) of deepsea samurai fish people. That is a different fantasy from a night elf. Especially if you give them a few unique anims like for vulpera.
Mechagnomes like in Wrath of the Lich King, or even a new type of robot gnome, would've offered a different fantasy from regular gnomes or gnome amputees.
That's the important thing for me. It offers something new, not just more of the same, or the same but more EXTREEEEM.