Τransfer data through AC signal
Your circuit might work, but you probably can't mix data and power. Since you'll be dimming the power line for data bits. One bit per fundamental cycle because you can't turn the triac off until a zero crossing.

PLC works by injecting a high frequency carrier into the power line. It uses a capacitive coupling and a bandpass filter. Look at the example circuits in the TDA5051A datasheet of how they inject and receive the 132.5 Khz signal.