Hmmm difficult. Npubs have a very complex checksum that is never used and very difficult for solid to compute.  It also is the wrong check sum (segwit, instead of taproot, doh!).  Npub would serve zero purpose here as we already have a nostr predicate.  Likely hex public key which is the canonical hex pubkey as better.  Npub is a mess of technical debt but is likely to stick around. 

 No idea on technical stuff.
 
I know with certainty that hex is worse from a user facing perspective. A bunch of seemingly random characters. 

Whereas npub is clearly associated with nostr. 

 in this case it already has the "nostr" part logically separated

the evolution of the web was from the hyperlink, to typed links

solid does typed links which is the most advanced form of the web, npub was a hack because nostr doesnt have typed links (yet) 

 hex is a terrible format, but great if you want to accidentally paste your private key instead 

 How is hex is a terrible format. It’s up to 255 in base16, good for hashes, exact length. Base32 is nice and so is base58.