You actually need a wayland server, since wayland is a protocol.
If you use a RDP client it doesn’t really matter to us if the other end is X11 or wayland, so no difference there.
OpenBSD still has their X11 server in base, for the other BSD’s they don’t seem too eager to “switch” and both will likely be supported for years to come, some linux distros are trying to push wayland, but even picking the latest ubuntu LTS still gets you X11.
A lot of the “X11 is insecure” stuff refers to vague stuff like apps beeing able to read the clipboard, capture the entire screen… which you can do just fine with our app_server, so dunno if we are “secure” by that metric either.
I’d be more concerned that X11 has deadlocks in the protocol you can trigger or so, if a user gets that accidentally that is extremely frustrating.
In any case, haiku needs neither X11 or wayland. Maybe once we have a gui frontend for remote desktops we will add an option for whatever protocol for that is popular in linux then, but even then we likely don’t need to understand anything of wayland.