How is that any more efficient that putting an (4.7 k/1 uF) RC LPF at the other end and reading it with analogRead ?
Actually, if you want to , there is no reason you can't use RS485 to send your data. I don't know why you chose to send PWM but you can still do that using RS485. Usually, data is sent using a protocol that involves a header, a packet and a checksum but that's beyond my level of S/W expertise. If I just needed to send an 8-bit value I would probably have to do it the same way you are, (because I don't know how to do it any other way , LOL).