Of note is, of course, that Wine already handles the 16-bit Windows API by mapping it (using some files containing API specs of arguments to replace) to its own

Of note is, of course, that Wine already handles the 16-bit Windows API by mapping it (using some files containing API specs of arguments to replace) to its own Windows API implementation already. It also seems to work under long mode, which implies that segmentation is handled through emulation or other compatibility behavior, as IIRC long mode does not even support segmentation in other execution modes.