What you lose is VT escape sequences, a hack to try to make TUI's when there was no alternative. In Plan9, your terminal windows naturally transition to be fully fledged GUI's when needed.
Also note that there is vt (at least on 9front), a terminal emulator for plan9, if you really want to use such applications. There's ssh too, if you need it.
A thing I forgot to mention: this means that if you "cpu" into another host, you can run text based commands, but you can also start the browser, mothra, or even doom in the same window. There is no difference between telnet and x forwarding on plan9.
Also note that there is vt (at least on 9front), a terminal emulator for plan9, if you really want to use such applications. There's ssh too, if you need it.