This seems a bit of an odd take. Matrix.org making their server freemium is up to them - charging some users to use the service (not the software) is a way of keeping the lights on. Better that than ads or selling user data. Lots of privacy focused orgs do the same - Proton, Tuta, Mailbox, Mullvad, IVPN. If people also have an issue with Element - don’t use Element, use one of the other apps.
If people are this upset, its not impossible (or even that hard) to migrate to a different server - or host your own.
Hard to see how them choosing to charge money to access their server will affect the future of the project, even them choosing to not run a free for anyone server any more wouldn’t necessarily affect the future of the project because the project is not to provide a free for all server but to develop software. Either way, them trying to find a way to keep the server operating certainly doesn’t mean ‘Matrix is cooked’.
As far as Redis goes, as I understand it, they moved their software away from an open source license. There’s zero indication Matrix are going to do the same thing.