Interesting story on the BI.   My friend, Dave Cane who had been #2 on the 780 and lead the 750 project was the primary force behind the BI and developed by the team in the laboratory products division (LDP).​  The whole idea behind BI was, BI was supposed to be (i.e. designed as) an 'open' bus and DEC was originally going to license the driver chips to a number of 3rd parties (I believe Western Digital, Mostek, TI).   The whole idea was to create a 3rd party market for I/O devices for LDP.   By making sure everyone use the same interface chips, their was a reasonable belief that the boards would not break bus protocol and have some of the issues that they had had with Omibus and Unibus.

But ... once the BI was completed and actually put into the 8800 and the main line system, DEC central marketing made it private and locked up.   Dave quit (his resignation letter was sent out on the engining mailing list -- KO and GB were not happy -- and one of the thing he sites is the fact that he thought taking the BI private was going to be bad).

FYI: Masscomp was formed shortly there after (my mostly ex-LDP, 750 and VMS folks) and Dave used MultiBus and later VMEbus for the I/O (but he did a private SMI like split transaction memory bus).

One of the other BI people, who's name now escapes me, although I can see his face in my mind, maybe I'll think of it later), would go on to do the PCI for Alpha a couple of years later.   As I said, DEC did manage to get that one public, after the BI was made private as Erik points out.