Not locking customization options to specific models would be relatively easy. Including additional pronouns (I'm assuming you're asking for more than just being able to choose he/she) could be burdensome unless there were a single third pronoun that would satisfy this need. I'm not up on non-binary terminology so pardon my ignorance if that come off as a confused statement.
More options are always to be encouraged, particularly with character creators and I think model swap stuff should be fairly straightforward. Certain unexpected roadblocks can sometimes turn-up with pronouns though: localisation being a major one. English is fairly gender-neutral, but a lot of European languages are gendered at every level, which does add a layer of complexity. I've seen this happen in practice at least once (the one occasion where I've seen a developer specify gender neutrality), where a gender-neutral term in English was localised across the continent in gendered terms.