While I don't agree that a draft is the solution to the "problem", I reckon it could potentially work in the NRL. But it would need to be in conjunction with a national youth competition (eg. Under 20s), a talent development reward system, more substantial salary cap concessions for developed and long serving players, and more transparent salaries for those outside the Top 30 squads.
There would also need to be regulations in place to stop players from taking back door deals and skipping the draft, or stop clubs from poaching draftees before they've played a game.
You cannot disincentivise clubs from developing players for their own gain. That would result in a lack of quality talent across the board. The NRL doesn't have the money or the systems to handle development.
But here's how I think a draft could work:
Keep existing junior competitions run through state affiliates - U15s, U17s & U19s. NRL clubs can choose to participate in these or not. Then all NRL clubs must have an U20s, with fixed price contracts for all players, eg. $90k.
At the end of the U20s season, each team is able to choose up to 5 players to sign for their reserves or NRL squad - for any price (within the salary cap obviously), and for any period of time.
Players not signed can nominate for the draft. Each club gets X number of drafts, with the order to be determined much like most US sports - a draft lottery.
Players signed via the draft have a fixed salary ($130k), and standard one year deals. For each player drafted, the club that they played Under 20s gets paid a nominal amount. This amount increases if they also came through other junior pathways with the same club. This amount paid by the new club, and subsidised by the NRL.
Players not drafted become free agents, and are able to be signed by anyone - again for a fixed salary ($110k) one year deal, and are only eligible for reserve grade deals.
Draftees and signed free agents would have an delayed trade window - that is, they are not able to signed from Nov 1 like everyone else - rather they are only free game after 1 July.
For me this would help keep things in balance. Development clubs have first crack at their gun players, they get kickbacks for every player they provide to another team, and there are rules in place to ensure clubs and players participate in the draft in good faith. Still allows for a more even spread of junior talent across the competition. And a well designed draft lottery system should stop teams from tanking to gain early draft picks.