You're missing something: IPv4 is not the only type of physical address supported by DNS. There is also IPv6, and historically there were others.
Instead of trying to parse the address and guess what protocol it might be, DNS tries to make that unambiguous: you ask it for the A or AAAA records for a domain name you are interested in, and you know for sure that you are getting an IPv4 or IPv6 address respectively.
The only clean alternative would have been to make an MXMXMXMX record type to hold a domain name OR an IPv6 address.
Instead of trying to parse the address and guess what protocol it might be, DNS tries to make that unambiguous: you ask it for the A or AAAA records for a domain name you are interested in, and you know for sure that you are getting an IPv4 or IPv6 address respectively.
The only clean alternative would have been to make an MXMXMXMX record type to hold a domain name OR an IPv6 address.