Another set of concerns is raised by the question of whether an identifier be human readable or not or have implicit semantics.
The reason the DNS is such a hotbed of political intrigue is that there are names like microsoft.com and there is an expectation that resolving such identifiers maps to the companies that have been using the names as trademarks.
Then there is the question of whether the identifier space is open or closed. There are only 65535 valid IP ports and so assignment or well known ports has different considerations to assignment of SRV tags which fulfill the same function.
IP addresses are also identifiers and there are different considerations for the different parts of the address. An IPv6 address must be globally unique and the upper 64 bits have to map to some form of routing information that is unique at a network level.
But another way to look at an IPv6 address is that it is a 64 bit address and a 96 bit port space.