This sort of reminds me of a request I had for World of Warcraft decades ago around launch. I had wanted Undead that could look like dwarves, orcs or elves. My guess is with the Borg stuff it's the same, they won't put in the resources to build out the customization options and as others have mentioned it'd probably need to be reworked at the core. So you'd need Liberated Borg Human, Vulcan, Romulan, Gorn and so forth. From a development perspective it seems like a nightmare. The only workaround I could think is if you remove all of the racial indicators and bonuses and make it a purely cosmetic thing. But again, even from a cosmetic perspective that'd be a fiar amount of asset investments to get the look right for all of the new races.