Development for Fenix 3 on ConnectIQ 2.2

I recently acquired a Fenix 3. I'm very pleased with it and would like to do some development for a wide range of devices. From what I gathered there are some issues with Fenix 3 and ConnectIQ 2.2. What I would like to know is if I have to develop in both 1.3 and 2.2 to have support for Fenix 3 and Fenix 5 (and newer models) so essentially it is two apps or can I develop in only one SDK. Also, what is Fenix 3 missing so that it can't have ConnectIQ 2.2 support?