You would have to somehow set a limit of legal expenses, which seems... difficult.
You would have to win to get the common fund, you may not get that far if you have to pay into the fund and amount a defense.
The litigants and defendants would not be compelled to contribute equal amounts. Just the disbursement would be equal.
If nothing compels them to, they won't, so effectively the status quo.
And Yuzu spends $25,000 and maybe wins the first case but runs out of money during the appeal and defaults judgment.
Nintendo gets the pot because they won right?
As I pointed out to another user, this reverses the damage if they win, but does not solve the problem of preventing them from being able to win.
Now if you make it where if you want to spend $5 on lawyer fees, you have to loan $5 to the other side and if the other side wins they don't have to pay it back, that may work.
That's essentially what I was suggesting with having to loan the opposing team the same amount of money you spend.