It'll probably be circumvented via signing-on and various other performance related bonuses. For example a player who would previously be offered £400k per week could easily be offered the new maximum salary and then £100k per goal plus £50k per appearance etc.
It is so easy to make bonuses ludicrously over inflated as there is nothing legally preventing it, but only the top percentile of wealthy clubs can afford to do it.
As you say, unless there is a TOTAL salary cap that takes into account ALL money changing hands from club to player for whatever reason at all, this is as doomed to fail as FFP was.
The signing on fee would be a sticky point as that could be part of the transfer fee which is separate from the wage budget but I’d imagine appearance/ goal/ assist/ clean sheet bonuses would all come under the wage side of things.

