It seems like their goal is to have a fully featured open source ecosystem that Core Devices (Eric's new company) builds hardware for. I don't think he's made any commitment on open source HW but you could sell your own pebbleOS devices if you wanted to (with maybe some effort required for radios or sensors that they can't legally open source code for).
Obviously he stands to benefit from the free labor, but the only reason the project makes any sense to start with is because of how many passionate hackers have kept the Pebble devices and community going. If they want to dedicate more free effort in exchange for the opportunity to buy hardware built this decade then it feels pretty fair to me.
I don't know if the hardware or any layer is patented.
Could I remake the watch, send over the software/firmware, and sell the watches legally?