Actually, If I recall correctly, Dallas came out with a device, based on the 8052, that brought out all 16 bits of address and all 8 bits of data bus as separate busses. The device was (and is) the DS5001fp. Still not quite true Harvard but getting there. By using the bytewide bus for external data (the chip also includes separate decoded strobes for the external stuff), you in effect have two separate busses.

A complete module, with 128K of static, battery backed RAM and a real time clock, was produced and called the DS2251T. I still use the thing as a development platform. It's great.