1. You can still use any code written before today under Apache 2 and build a proprietary version out of that.
2. If you'd like to build a proprietary tool that makes use of the new features Element builds after today, you can do that as well if you negotiate with Element.
But you won't be able to use any of the new work Element does on Synapse after today without either open sourcing your project or paying Element.
The CLA gives them the ability to relicense, which affects proprietary products built on top of Synapse/Dendrite. Without the CLA, all code written against the AGPL-licensed Synapse/Dendrite would have to be licensed AGPL as well, even if it interacts with Synapse/Dendrite over network boundaries as part of a SAAS offering or somesuch.
I believe that's why 'AGPL' is a four letter word in certain circles.
No, that's a common misconception. The relevant section of the license is:
> Notwithstanding any other provision of this License, if you modify the Program, your modified version must prominently offer all users interacting with it remotely through a computer network (if your version supports such interaction) an opportunity to receive the Corresponding Source of your version by providing access to the Corresponding Source from a network server at no charge, through some standard or customary means of facilitating copying of software.
This does not state that you must license any of your software that interacts with the AGPL code over the network as AGPL, merely that you make modified versions of the AGPL code available to users who interact with it over the network licensed as AGPL. The rest of the license generally behaves as the GPL would.
