I'm not aware of a RIOT port for one of these boards. Porting the Photon shouldn’t be too difficult as it seems pretty similar to the spark and has a CPU of the stm32 family which is well supported in RIOT. So if you have any aims for porting, we'll do our best to support you . But please note that if you're interested in WiFi there might be other gaps as we focus on 802.15.4 radios.
I don't know your concrete requirements but did you check the remote, z1, cc2650stk, phyNODE (in RIOT pba-d-01-kw2x), mulle or limifrog boards? Also some STM boards do have on-board sensors. But before you make your choice, be sure that all drivers you need do exist.
Generally you could use "any" board and make it with cable-connected sensors.
regarding the Onion Omega: I personally own 2 of these boards and they run a variant of OpenWRT-Linux by default. They have an ARM-CPU running @400 MHz, 64MB RAM, and 16MB flash + Wifi 802.11 bgn, BT-LE is optional. IMHO this is kind of a big iron to run RIOT on, and why would one do that when it's capable to run _real_ Linux? I think it's closer to a RasPi than to a RIOT board.
Nevertheless the Omega is an interesting platform e.g. to work as boarder router/gateway, as an alternative to the RasPi+Openlabs setup. Maybe we should suggest an 802.15.4 extension to the Omega developers, would be nice having that ...