Adam/Dave,
For whatever's it's worth, in PC/AT ISA bus times, at least one of the serial port vendors (RocketPort was the vendor IIRC), used a DB-52P connector, that connected to an interesting 'tail' which had 8 DB25P connected to the DB25-S at the other end. This allowed 6 data conductors (RCV/XMT/RTS/CTS/CD/DTR) * 8 ports, plus 6 grounds which again IIRC they interspersed among the remaining 6 ground pins.
What I remember is that it was this specific board that was one of only a handful serial boards[1] that could run UNIX properly and hang Trailblazer modems off of it because they not only fully pinned, but they had single-chip custom USART with a good bit of buffering and hardware-based RTS/CTS flow control. I think I may still have one somewhere, as I saw the cable for it when I was looking for something else over the Christmas holidays.
[1] The original PC/AT used the NS8250 UART with no input buffering, which went through a couple of generations, eventually begat the *550 version and had I think an 8 character input buffer. But IIRC none of them had hardware flow control. I forget the # now, Moto made a nice dual UART with 16 chars of input buffering, that many of us on Unix workstation business used, but when we moved to BSD 386 and Linux, we were stuck with PC hardware, which had a particularly hard time with things like the Trailblazer (which was the modem of choice for UUCP).
Clem