I can't understand why are we even talking about Thiago? If Koeman wants Wijnaldum than we should try to get him and not some other guy that coach doesn't need or want.
Messigician is right.
Koeman is appointed by a board that can be ousted in less than a year and will prolly come with their own coach. Or Koeman might be out even if the current board is reelected. You can bring him players fitting the profiles he need but you don't necessarily need to buy a specific player.
Wijnaldum isn't exactly a world beater either, although a good player, and isn't young anymore.
I have seen some clubs being burdened with players chosen by ex coaches and not being in line with the new sporting project of the new coach. If you let the final choice to your Director of Football (Sporting Director or whatever way you name it), you mitigate the risks.