Downsides to making a common type like URL conform to Identifiable?

[SDGGiesbrecht (Jeremy David Giesbrecht)]

This is called a retroactive conformance and you can read the nuances here:

Retroactive Conformances vs. Swift-in-the-OS

Let's start with the following definition... Retroactive conformance: extending a class, struct, or enum from another module to conform to a protocol from another module. The protocol and the conforming type may be from the same module or from different modules; the important note is that neither is in the same module as the extension. Hopefully uncontroversial. Retroactive conformances are a useful feature, mainly because (as Dave A has said in the past) they allow you to take types from on…

And yes, the airtight solution is to wrap it in another type like you have both demonstrated.