The number one reason against is wxWidgets would easily double the size of the BlitzMax installation file and from memory triple the time to rebuild all modules. The FLTK library is not pretty but it is beautifully small.
From what I've seen on Linux I'd vote Mono as the best target in regards to the next MaxGUI driver.
In regards to the original post, it depends on what type of application you are building. If it is an audio app with lots of sexy knobs or something that could benefit from lots of transparancy then you could consider one of the third party GUIs built with Max2D or raw OpenGL.
From what I've seen on Linux I'd vote Mono as the best target in regards to the next MaxGUI driver.
In regards to the original post, it depends on what type of application you are building. If it is an audio app with lots of sexy knobs or something that could benefit from lots of transparancy then you could consider one of the third party GUIs built with Max2D or raw OpenGL.