Four tuner premiers and all Roamios have a Moca adapter/bridge built in.
When you get a Moca adapter, it provides you with an Ethernet jack to plug devices into, basically bridging the two networks. Networking setup at that point from inside the premiere is essentially the same as if it was on an all-Ethernet network.
Are you currently using the Roamio to bridge the networks? Getting a router that can provide a Moca bridge will simply move the point where the bridge is. It would then give you the choice to connect your Roamio to connect via either network. Just don't leave it connected to both in this configuration, as having two active bridges causes packet routing chaos.
The premiere would still ether need Ethernet run to it, or a bridge to provide it with Ethernet since it doesn't have Moca functionality built in. Note that with a Ethernet switch added, you can even share this networking with other devices in that space.
Also, the moca bridges work "both ways", so if you got a router with a Moca bridge built-in and connect to your router via moca, you could use the Ethernet jack on the Roamio to provide networking to other devices in the area.
Note that the mini is the other variant in functionality, since it can connect via Ethernet or Moca networking, but it can't bridge the networks the way the full tivos can.
-Roamio Pro/Slide Pro
-Stream (Gotta go unplug the sucker one of these days!)