> but it would have made extending the address space further much simpler.

Given published information [1] that the 8086 was designed in a weekend as a panic stop-gap to provide some form of "more advanced CPU" to keep Intel in the market while the iapx432 project was underway, but falling far behind schedule, it seems doubtful that the designers would also have been thinking of "ease of further expansion for future revision" on what was, at the time, just a stop-gap CPU to sell while awaiting the shipment of the iapx432. Published information is that at the time Intel never expected the 8086 to create the huge extended family it has created, and instead expected the iapx432 to be that "grand family ancestor". The market, of course, had other ideas, and IBM's choice of 8088 for the IBM-PC was the catalyst that launched the 8086 design into the family it is today.

[1] I no longer have a reference to the publication