Tamils also have an earlier UU.To just quickly return to the suggested civ:
The proposed UU would be a replacement of the machine gun but with the current idea it does neither fit with the tech requirements nor the resources of the normal machine gun.
Would it be possible to do something like the Indonesian UU? To take the unit and make it accessible much earlier, actually make something totally new out of it? Or would that be off limits?
Of course, if implemented, the Boers would need a horse close to their core area that spawns with them.
By the way, I would be more than willing to compose a list of Great People, city renaming (actually just translating the Dutch names into Afrikaans) and so on for that new civ.
If is is to replace Machine Gun then it should have 14-15

Boers brought their horse from abroad and bred them on a small scale level there.
TL;DR
Might as well add Canada and Australia at this point.
Definitely not Canada as that makes it too easy for US.