@serebit @element @maxgot @schmittlauch @matrix Since Qt is explicitly mentioned: Have you considered the QPL instead of AGPLv3+CLA? This also gives you permission to include patches from others in your proprietary distribution - as long as you keep Synapse open source. This would address 2 of the major concerns: Signing a CLA and Element making Synapse fully proprietary.
On top of that, you could even have something like the KDE agreement, where if you fail to release source, the last release becomes MIT-licensed.