What a terrible proposal. First, the correct solution is IPv6 and not this hack. Second, why would you even start by suggesting that only some HTTP clients support this? To make my life more difficult because e.g. curl supports this but Chrome doesn’t do that debugging is harder? Would a browser that does support it hide the fact that I am connecting to a non-standard port so that when I do take the URL to a library that does not support this that it would fail with “Connection refused” for no discernible reason?

This is straight up awful.