My problem with IPv6 is that I can't double click 2001:db8::1428:57ab to select the entire address. It's a silly complaint but representative of real ergonomic issues.
The hard part is to find all the places to repeat that change, and convince the code owners to accept it. Probably start with a standard analogous to RFC 5952?
"A: B" would still click-select either "A:" or "B", but "1:2" (a ratio) would select the whole thing, as would "small:med:large" or an ipv6 address. In other words, I think that, in practice, English writing has assigned semantic significance to space-less colons in enough cases that text selection systems should reflect that.
Though I'm not sure RFCs are going to drive general GUI behavior--they won't "MUST" it, because that's overstepping, and I'm not sure GUI/OS-text-selection-functionality maintainers will be persuaded otherwise.