I'm not sure if you're actually asking for an opinion or not
but I'll offer my two cents anyway, because I'm nice like that, and my fingers need the exercise
This is such a personal decision it's very hard to even know what to suggest. I guess all I can say is that if you meet the conditions they are asking for, it's going to improve your physical condition anyway I should think, so I see no reason to not do that stuff just for yourself. If/when they call with an offer, you can still say no if you decide you're not ready, or have changed your mind. It is probably a good thing to have that opinion there.
I know you said they won't transplant post 70, and I'm not sure how old you are, but I will assume from the context that you're headed there. Yes, that is definitely an issue to consider as well... plus your current quality of life (are you happy with dialysis? does it give you the freedom you want/need?).
Nobody but you can answer these questions in terms of the potential benefits to you, vs the cost (and going through a major operation like that). It would probably be worth sitting with your neph and discussing these thoughts with them to get their perspective and making an informed judgement.
Whatever you choose, best of luck!