Not that I think he would get paid, or even 'demand' that much, but actual number aside, why?
Does it rock the apple cart any more than another club paying a player that? Do players negotiating wages not think I could be getting X elsewhere, look at what Y is getting paid?
What is our limit, Kdb's wages? If he gets a pay rise in a new contract, does everyone get a pay rise or the right to ask for one. Or maybe we strike a midway point between zinchenko and kdb and thats what everyone gets, existing and new.
If my employer was to bring someone in, and pay them more than me to attract them from somewhere else, would I be annoyed? If they were doing the exact same as me, potentially, but if they were doing more, better, or bringing in more revenue, I'd either shrug and carry on or try improve.
Longer term, I think not going over some arbitrary imaginary wage cap to bring in top players would be more damaging than doing it here and there. Because what top player with a choice of top clubs would go for the one known to never pay more than their current set limit.