Alonso is a very intelligent guy, he was a fantastic footballer too so my early thoughts are that he will do well at Real Madrid.
The thing is though, Real do not accept failure. He needs to start well or the pressure will seriously on.
Just give Xabi a try to handle the club. We won't know the result without having him sitting as a head coach of RM. Absolutely agree about how Madrid is impatient club who often sacked coach when he's not deiiver. This reminds me with Benitez, Lopetegui, and Solari who being sacked just a few months after being appointed by RM.
Xabi may also have the same fate like them all if he can't be successful on his first year. However, let him do something to sort out all of pressures he receives at his first season. Kinda unfair when we judge him even before he delivers.