I suppose by "SDK for Wine" he means winelib. This library is useful if the developer doesn't want to reimplement any used Win32 API functions. This is not really the problem with WME, the graphics part is (game engines typically don't use a lot of WinAPI). As far as I know WME games DO work under wine (with some tweaking involved, of course). What doesn't work well are 3D characters, and especially shadows, because the wine implementation of Direct3D isn't complete (neither AGS or Sludge use D3D btw). winelib wouldn't help here at all.
An ideal solution would be to write a second renderer based on OpenGL (and also a second sound system, a second X file parser etc.) And once written, they'd need to be supported. All changes to the render/soundsystem/etc. would need to be done and tested twice. That's something I don't have the time or resources for. And THAT's the problem here. That's why I concentrate on the most viable platform. ad7enture can sue me, but that's the way it is. By the way, the Linux port of AGS isn't being developed/maintained by Chris Jones.
Another thing is, you want to use the *tools* under Linux as well. In this case a Linux port would mean "rewrite from scratch" I'm afraid.