I grew up with a "Siemens PC-D", 80186 and not fully IBM compatible for the reasons you said. However, it seems that the folks at Siemens were very enthusiastic

I grew up with a "Siemens PC-D", 80186 and not fully IBM compatible for the reasons you said. However, it seems that the folks at Siemens were very enthusiastic about it, and ported a lot of software that accessed the hardware more directly, including most Microsoft software (Windows, Word, the C compiler...) and GEM. The BIOS was actually on disk, so updatable, and the BIOS updates came with a README file from the PC-D team that again give me the impression that some at least really liked working on it. A marvelous machine. High resolution (if monochrome), Hercules-like graphics, for example. But the kicker was that it actually had an MMU[1], built from discrete logic chips, in order to run SINIX (a Xenix 8086 derivate, but with added MMU support among other things) and enjoy full memory protection. I reverse engineered that MMU, it's quite fun. Paging wasn't possible though. [1] Early on as a variant called "PC-X", but they apparently did away with the early board revisions, and all machines I've seen say "PC-D/PC-X" on the back, so they all have the MMU and can be both.