The answer would be a definitive No.
The main issue is that cooling on the Rock Pi X is done under the SBC, while on a RasPi cooling would be done on top, since the main CPU for each is on opposite sides of the board. If you didn’t care about cooling, then you could make a RasPi 4 case work, cutting an opening for the full sized HDMI, but then your X would be thermal throttling all the time.
About the only “cases” you could currently use between the two are simple acrylic sheets on the top and bottom, using the existing pattern of standoffs, with sides that are open. Basically a “sandwich” type case.
I’d love to see a Flirc-style metal case though. It would reduce the height since the case is replacing the heatsink itself.