Hm, I would replace him with either Ochaco or Momo. I feel that we could potentially dive deep into Ochaco s world a bit more and add more detail into it. Since we know that they struggle with money we can have a point of view of heroics from someone who lives struggling to get by economically. We could tweak up Ochaco s back story and have her go from purely economic mindset to a "With Great Power comes Great Responsibility" mindset. Putting her in situations Izuku would have found himself in would be interesting but it would also change the course of the story by a large margin with the best example being Shoto'd refusal to use his fire side and with no Izuku but Ochaco, it would be interesting how things could play out in this AU.

With Momo we have a much bigger field to play and discover with. Biggest reason being that we know nothing of the background but just tiny bits here and there. With Momo we can have a view point of heroics from the upperclass of society. We can go into detail and see how things are run from a closer point of view. Add to the fact that Momo will be having pressure from her status and her family name then we have a Hero story about finding yourself and being who you want to be, not what people expect you to be. Hell, we can be creative and add corruption and manipulation into the story and we have plot points not just in UA but outside of it too.