If your only goal is to reduce bots, then yes it should be successful. However, this limits the amount of time people can spend on the app. Which is the antithesis of what a successful social media platform wants to do and what ad agencies what to do.
Ultimately if he sticks with this it's going to be a death blow for the platform.
I don't see how this limits bots at all. You can simply spin up a hundred thousand bots and you'll be able to crawl 30 million posts a day. At best it will slow bots down for a week while they refactor how their systems work.
Supposedly if you spend about 10 minutes reading tweets, skimming through replies, etc, you'll hit the 300 post limit and be unable to use the app until the next day. Only letting people use the site for 10 minutes is clearly bad. And most people just are not going to pay to be able to use the app.
I'm not familiar with Twitter, but putting a cap on how much content you can view on a social media website doesn't seem like a smart move. If people are seriously doom-scrollers and hit the wall, they won't be happy. "Free speech absolutists" will be pissed when they see that there's a limit to their access to "free speech." Involving paid teirs also looks greedy.
All of that aside, there are better ways to fight bots rather than limiting their daily access. Bots will still be able to scrape a large amount of data daily. Why put a cap on how many posts you can view in a day instead of detecting accounts who are viewing posts at a much higher speed? I doubt most human users will interact at the speed of a bot, and the accounts who do can be verified as real.
Writing a code to detect bots is harder than putting a usage cap, though. That would require employees and Musk actually asking for someone to do something he can't.