Just installed three of these 1U dual-1:8 RF-mutliplexers in the lab to make a 40-channel 1PPS measurement system. These are built by Aivon.
Time will tell how robust these are and if there are any failures in continuous use... Initial results from the field are good however.
We connect these in a depth-2 tree. One 1:8 mux is the top-level switch, with the remaining 5 providing 40 input-channels. This easily expands to 64 channels by adding one more 1U box. Beyond that I guess a depth-3 tree connection is required.