It is certainly possible but the bootloader is closed so a clone would need to buy them from PJRC
Once your design is settled and no longer needs an in situ bootloader you can make a programer stick with a bootloader and program multiple boards with it. Or just transition to direct JTAG download of code you prototyped on a teensy.
There should be no license issues with the Teensy core but you would need to check libraries you may be using.
I would need a way yo let customers do a firmware update from a PC via USB. Can I use a different open bootloader for that? (just flashing a binary image)?
There are a couple of ways to write your own code that support self updating, unsure which if any are active at the moment (search for OTA updates and/or utasker http://www.utasker.com/kinetis/TEENSY_3.1.html) Not aware of any that are plug and play unfortunately.