Actually, there is an easy way to do this. You could dedicate one Hubitat hub to be the "master" hub. It's job would be to run part of your system via radio, and all of it via LAN link with another hub. There is a simple app you install on the "slave" hub, that forwards events to the master hub. So all of your devices show up on the master hub, and your automations would run there. This would keep your radio clusters small as you like.
FWIW, I have about 80 z-wave devices on my hub, and they are all snappy fast. But, please let me encourage you to only put 50 on yours and use a second and third Hubitat hub!! 
This same technique can be used to link ST to Hubitat, to run a blended system during migration.
