It's for when we'll use a new kind of addresses, e.g. when we'll use addresses version 2, it would be useful to send coins to old addresses...
Also, testnet coins sent to bitcoin address are easily retrievable, I made a guide about that
Well sorry but it wasn't all that clear to me. A new address version would seem to need a lot more code than just <= version and it is a hypothetical future use as opposed to the implemented current use of the version byte
I understand how you can just switch wallets around to retrieve the "lost" coins but if the sent to address isn't yours it may not be as easy as you make it sound.
True they're "just" testnet coins lost, no big deal I suppose but I still found it inconvenient and it just seems like a simple fix and the objections are rather abstract/hypothetical.