JonDo project was not dead: Portable version: https://anonymous-proxy-servers.net/en/jondofox.htm Integration of Tor and Jondo is a very interesting feature IMO.
Why would anyone ever pick Jondo over Tor Browser if the goal is to use... Tor? I don't really feel confident in the project when the link dies. They rarely if ever updated their browser in the past, so who's to say it's well supported now? To top it all off there's a typo in the first line of the announcement
I think this is more a recognition of the amount of work required to lock down FF to the required standards, and the popularity of TTB. Seems to me that adding Jondo to that is better than trying to roll-their-own. Plus you get the anonymity benefits of being one-of-TBB. So, for anyone who wants to pick and choose, they can, and it's no-cost to the developers. If they focus mainly on their core protocols, I think that's best.
JonDo is cool, and can complement both VPNs and Tor. It's a little on the small side, however. Smaller than I2P, even. And the mix thing is more about deniability than "anonymity", I think.