Not sure this is really anything new tbh man. Been happening since the bosman ruling came into place with very, very high profile players too. The only reason its happening now is because of PSG's/Mbappe circumstances, with PSG essentially being in a league with no real pulling power, combined with Mbappe being young enough for it to not be a big deal to bide his time there too. Also the market. It got so high due to PSG's ridiculous Neymar fee that there was no feasible way anyone could sell Mbappe for loads less (despite Madrid's really high bids being insane, but nowhere near PSG's Neymar price) as they'd have to essentially admit that they overpaid themselves, so Mbappe's only option was to wait his contract out really.
He was only on a four year contract too, which was sorta short, but it was because he joined as an 18 year old I guess. Most stars are on five years, and most usually won't want to wait around for ages to get a big pay day when they can still get it half way through their contract and fuck off. Short career after all and you never know where you'll be in a couple of years. I don't think this is gonna be a big change personally. The game's skint right now due to covid, but i think we'll be back where we were in a couple of years.