As a possible solution to the Toxcore licensing issue raised on Github, I would propose the option to ask the toxcore contributors to switch from GPL to the LGPL license.
Please see my comment on GitHub: https://github.com/elastos/Elastos.NET.Carrier.Native.SDK/issues/176
LGPL states: “a larger work using the licensed work through interfaces provided by the licensed work may be distributed under different terms and without source code for the larger work.”
In that case, even if toxcore is LGPL, Elastos Carrier may keep the MIT license.
The question is however, if Elastos has planned to modify the toxcore library that is used in the Native Carrier, as it would go against LGPL license as well.