I've been pondering the possibility of using pinChangeInterrupt with the AltSoftSerial library (at least until I can get down to a single serial device.
My thinking would be to change the mask to allow the interrupt on the software RX pin the instruction before sleep, and to have an ISR that rally does nothing more than disable the interrupt now that it's awake.
at 9600 baud, there's over 100us before the next bit, or around a thousand instructions at 8mhz.
Is this likely to work? And if that's not fast enough, would always leading with a sacrificial character help?