There’s security, privacy, philosophical, and practical implications with using Nostr for all of these things.  From a privacy perspective, it’s not particularly private to associate everything in your life with this one identity.

From a security perspective, it’s a danger to tie everything you own or do, the sum of your entire life, to a single private key that you could accidentally compromise.

From a philosophical perspective, there exists the possibility that some will wish to use other systems to transmit data.  Such as Nostr relays using cloudflare, or the focus on custodial cloudflare “bitcoin” bank accounts.

From a practical perspective, what vendors sell SIM cards based on Nostr identity?  Wouldn’t you want to hide this from the provider? 

 Bar the SIM concerns (all corners you raised are valid FYI) ... could this be a multi-sig problem? i.e. why would you only make one Nostr private key for all these N solutions .. why not N private keys?