Besides OpenGL and OpenAL the engine uses no external libraries and its reliance on any kind of OS functionality is truly minimal so I would expect it to be fairly painless.
http://www.gog.com/news/gogcom_soon_on_more_platforms
@Gilrond and @Volsung must be partying hard right about now.
Good news!
No, don't duck. This is actually good news
Fantastic news and a wonderful b-day present. Thanks GOG!