I think this really will be the straw that broke the camels back for a lot of people. I don't think it will immediately kill twitter but it will have a lasting effect. And if not this I am sure he will come up with an even worse policy change within the next 2 months. Something like limiting it to only 10 tweets per day for unverified users.
Everyone in the world who uses Twitter to broadcast news to the masses now can’t. Every news org, company, and politician now has dramatically reduced incentive to post on Twitter.
Much more importantly, advertisers and marketers have less incentive to invest time and money in the platform if people are being rate limited and forced to make accounts just to see the ads.