The problem with that LB, is that an underperforming national team would create greater incentives to go overseas for the big dollars. You get a situation where it becomes a downward spiral, with poorer performances creating a lower income for players, more top players head overseas for bigger money, the national teams performances fall further, plus less top players on exhibition, crowds and sponsorships fall, and so the spiral continues.
Domestically it would mean the Tahs and the Reds, who attract bigger crowds and bigger sponsorship dollars, would attract the better players and so get relatively stronger. They too, however, would decline for the reasons stated above.
From a budgeting perspective it makes sense, but top payers would see themselves attracting less and less money as performances declined due to the lower standard of players around them.
I have a real estate agency, where commission payments are based on individual performance. If commission payments were based on the entire teams performance, the best salespeople would all quickly move to the top performing agency, it's market share would increase and the others fall further behind. When individuals get paid by their own performance, the number three agency can become number one if they get it right, as top performers are happy staying where they are as long as they're happy with their conditions and the culture, because they still have no limitations on their earning capacity.