The biggest problem I see with it is that only some plat and some Gold teams would even attempt it and that is only if they still get a prize at the end and the medals that valve gives after each season.
If the prem from 6's also transfers over to highlander then I don't think it would be that huge of a income increase unless players would have to pay for highlander and 6's separately which means I certainly would not be playing ESEA highlander. Seeing as most plat and gold teams have ESEA players in them if they would have to pay separately for highlander then no way that is happening and if they don't have to pay separately then I can only see ESEA losing money.
Also if a team wins and there is a cash prize each player will win less money so it would only make sense to have 12 or fewer people on your team with 9 starters and 3 back ups max.
The only way I can see this working is if ESEA can also get Euro teams in the same league which means matches with people having 360 ping while the other team has 30 ping. There would be more money, more teams, and more lag.
It just wouldn't work out, sorry mate.