Comment by myself248
"Big ears, small mouth" is exactly what the regulations are designed to encourage, so I don't foresee regulatory issues.
You don't even need extra hardware for the duplexing; the common SX1276 chip has separate Tx and Rx pins which are typically combined on the PCB. All you need is to route a PCB that brings 'em out separately, if that's what you want to do.
In practice it's tricky to aim two dishes the exact same place, so using a single dish with a single antenna at its focus is probably quite a bit more practical. The SX1276 also has a PA control pin, invert that and you've got your LNA control signal. Or don't bother with the LNA, and simply mount the transceiver at the focus to minimize RF feedline losses. You'd give up a smidgen of performance but gain a lot of simplicity. (There would still be coax running down the boom, but it would be carrying the wifi/bluetooth signal outside the dish's aperture!)
I didn't know about the chip having separate TX and RX pins. There must be a gap in the market for rooftop-to-rooftop LoRa transceivers that don't cost a fortune. Even using something like a 24 dB gain antenna would push range up by a factor of 10 relative to a simple 4 dB antenna, or get a substantial improvement in bandwidth/reliability at the same range. For an even simpler design, you could just put a 20 dB attenuator between the transmit port and the antenna, reducing the effective forward gain of 4 dB, while getting the full 24 dB in the opposite direction. Proper RF engineering details an exercise for the student etc.