This isn't strictly about ble mesh but hopefully fits with this thread.
The Bluz DK and Bluz Gateway shield made it capable of connecting a BLE only node to the Particle cloud, including OTA updating the BLE board via the gateway. As I understand it, the Bluz DK was essentially (and ironically) a xenon that communicated over BLE instead of Thread. (not BLE mesh though, the Bluz had an nrf51822)
This was before Gen3 hardware so the Bluz gateway shield was necessary to add BLE support to a Photon or Electron. With Gen3 boards, you should have been able to skip the gateway shield and connect a Bluz DK to the cloud directly through an Argon or Boron. I say should because Bluz was considered to be superseded by particle mesh and was depreciated.
So now we are in a situation where Particle built xenons are less functional than the Bluz DKs which they superseded.
Additionally, the Bluz DKs could use a smartphone app as a pseudo gateway to the Particle cloud (pseudo because it didn't 'cloud connect' the end device to provide OTA updates, it just acted as a mitm to publish/receive event on behalf - I think) This would still be possible with a xenon and the Particle SDK however as you won't be able to register new xenons it won't be an option going forward?
If it was possible to combine the particle BLE update feature @ScruffR mentioned above with the Particle SKD to pass events to and from the xenon that would be a fully fledged gateway app akin to nrfcloud which I am sure there would be interest in.
Obviously the addition of BLE mesh would perfect, but for me, a star configuration capable of pushing updates to xenon nodes from a Boron (just like Bluz did) would be more than enough. To quote from the mesh depreciation thread..
sure there are a few (somewhat arduino compatible) nRF boards around but as far as I'm aware there's still not an OTA solution out there that matches up to the Bluz/Particle solution in terms of ease.
note - i never owned a Bluz so please correct me if I've got it wrong on anything above, thanks.