I worked on a project that used "regular old URL" just like you suggest, for contract and service identifiers, which needed to be human read/write/generatable

Tag URIs would have been better because:

a) not everyone owns a domain, but tags allow email address as authority

b) it's confusing to many people to overload http URIs this way

c) as a contract identifier the URI doesn't need to point to anything, but this creates cognitive dissonance — this is probably part of b)

d) too damn long — tag URIs might suffer from this too. We were using these all over the place and there's no good way to truncate them