1. AT&T started with S4 and continued the tradition there after (G2, N3 etc.) (Also no dev edition AFAIK)
2. T-Mobile started with LG G Flex and looks like it will continue the tradition with S5. (Source) (Also no dev edition AFAIK)
3. Verizon started who knows when? (At least verizon is nice enough to have Dev edition, albeit expensive as hell).
What does all this mean?
Well you can't have "traditional" custom recovery so that means NO ASOP, NO custom Kernels etc.
You can have a recovery called "Safestrap" which will allow you to flash only TW based ROMs and simple MODs such as bootanimations but nothing more.