Future? Existing Product? I would like a Wifi that can fail over to LTE

For my application I would like to be able to connect Wifi most of the time but have a Cellular fail-over. In WiFi mode I would send hourly usage stats to provide the user with up-to-date information over the web. But if (when) wifi, that is being provided by the end customer, goes down, I would like to fail over to weekly summary reports/maintenance required reports over cellular. Does a Wifi+LTE product exist yet? Is it in the plan for Particle? For the moment, does Boron have a “borrow my connection”, so that Argon or Photon can use the connection over uart?