You ask,
"What does your "convenience" matter?. The issue is a well designed product, not something that is convenient for the designer."

and the answer is, well, a truly well-designed product is one that serves the end user, and not necessarily the designer.

and you go on to say,
"the UART is virtually never used in mode 0, so the xtal discussion is not directed there."

While that may be true most of the time, in this case, the ONLY excuse for using an 805x is that it has a synchronous serial channel, so mode0 is essential. The MCU's I'd prefer to use don't have synchronous capability at a high enough rate to serve my needs, and bit-banging is completely out of the question.

Nevertheless, since it's possible to get all the popular baud rates above and including 4800 from a 12 MHz crystal, and derive other benefits associated with precise timing from that as a timebase, I think it's worth a look.

If I were doing something for my own convenience, I'd use an external UART for a console and be done with the question altogether. That's what my development environment does. It uses an SCN2691 and 75155 for its serial port. That whole thing fits on a 32-pin skinnydip site. That way all the timers and both the serial ports on the MCU are available for target use in whatever mode I choose. The on-chip UART shouldn't be the console interface anyway, should it? What if you need the thing for useful work?

RE