Loaning players can work, especially if teams lose key players to injuries in pre season.
However, I think the NRL is better off with a draft and trade system than a loan system. I think junior leagues should be run completely independent to NRL clubs, right now you've got only a handful of clubs who prioritise youth development and I think it's shows with the lack of quality players around. It should be run similar to the NBA, each team is given draft picks and they can use them how they see best.
That way the junior players can be put through a better system to aid their development, they could be better educated with how to deal with social media and the pressures of the game as they would be the main priority of the clubs, instead of first grade.
That way you wont have teams like Melbourne ending up with 3 of the best hookers in the comp, or Panthers have 4 first grade quality halfs whilst we have none.
Financially it may be challenging at first but it would open up so many opportunities for the game, imagine the hype they could build for the Nrl Nines after a draft in the off season, they would market it as the first chance clubs get to see their new young stars in their colours. Imagine a team like ours, we wouldnt have to sit through a 4 year rebuild, we wouldn't have to lose the likes of Klemmer for nothing, we could trade him away for a draft pick etc.