I agree, but I think the scheme puts too much control in the hands of a central organization that has a vested interest in keeping things clean. On the one hand, it will block candidates out or, on the other hand, it will allow candidates to come in because the cash is available for all. You're stuck on both ends. If you're the candidate, one reason we run for political parties is for the benefit that gives us: you give up a bit of control and they sign off on your loan, subject to the risk.
Nomination and leadership contests are altogether different beasts; they're contests among individuals. We've seen examples already in which, at the nomination level, boards and parties have favourites and have candidates they would rather not have in the contest. I worry that if we give them tools to disallow them, it's going to narrow the scope of candidates. At the other extreme, opening it up too far would bring forward candidates who are running simply because someone else is going to pay the bill.