For point 1 I can try it... just a question : the directives in import.ext are processed sequentially ?
I mean :

files somefolder/*.cpp;
exclude somefolder/platforms/*;
files somefolder/platforms/posix/*.cpp;

will pull in all somefolder cpp files, excluding somefolder/plaforms folders but including somefolder/plaforms/posix folders ?

For point 2, I see it more difficult without tampering with all build system.