Does OS/2 4.52 support both S/VGA and MDA at the same time? Are there existing drivers for it?
Yes it does, you may have to some digging around for the driver, might be on hobbes, text only if I remember it correctly, but i used it for years for text editing as the old MDA screens were much sharper than the SVGA screens of the day.
It has limited use for debugging purposes however since the IBM debugger has already started to communicate via the serial port long before the MDA driver is initialised, so having a small computer such as an old thin client or an embedded industrial platform that you can get off ebay for 5 euros, act as a serial data logger makes much more sense.