As far as I remember, isn't it required to make the license GPL for all the plugins hosted at wordpress.org? Since the demo plugin uses some GPL licensed components such as the markdown library, the demo plugin cannot change the license type other than GPL.
However, the framework library itself only uses a MIT licensed jQuery plugin as an external component. The demo plugin is just for demonstrating the use of the library. So it might be possible to apply a new license type to the framework library files separately. And I don't mind doing so.
By the way, if you are planning to include the framework, it is recommended to use v3 as it has breaking changes and not compatible with v2.