I have finally made up my mind and decided to use Supermon816 as the base for the monitor of Lilith.
This meant I had to “rewrite” the source for ca65 (part of cc65), as that is the assembler I use/prefer.

Currently I have a working monitor, with an Intel Hex upload routine (with a small bug remaining). This routine is based on code found at http://www.6502.org/source/monitors/intelhex/intelhex.htm

Also I have added a 16×2 LCD (HD44780 compatible), which is driven using a 6522 VIA, based on the design by Ben Eater. I intend to move from an 8 bit interface to a 4 bit interface, so I have some additional pins free of the 6522 for other purposes?

I am planning to publish the complete project in the near (very near) future on Github, but I have to do some housekeeping before I do. The folderstructure is a complete mess right now.
The project on Github will contain both the hardware design files (Kicad) and the sources (both 65816 assembly and GAL PALASM sources).