Btw.: does the MEGA65 have an buffered RTC onboard?
If not: would it be difficult to add the cassette-port on Board Rev. II or the MEGA 'AT' ;)
Because in my opinion, that port is not so useless as CBM tought. They used it only for tapes, but in real life there were many add-ons that used the cassette-port, especialy using i2c system, for RTC, and temperature-sensors, or similar.