Good requirements definition greatly simplifies a project and provides clear metrics for success so here we go:

Minimum requirements

1. Create transmitter and a receiver devices for taking a digital serial signal between 900kHz and 1MHz and overlaying that onto DC power.

2. Make the devices small so that they can be installed on each LED strip

3. Make the devices daisy-chainable so that a receiver feeds one LED strip data and power and then that LED strip can feed a transmitter to send data to the next LED strip in the chain.

Nice-to-haves

1. Make the devices cheap and easy to solder to the ends of LED strips

2. Find a nice cable (waterproof?) to go between LED strips

3. Make the devices handle lots of current - up to 5 or 10 amps - so that lots of LEDs can be driven in series. Alternately, make sure power can be injected into the LED strips at regular intervals.