I think the original plan was for Twitter to adopt AT Protocol so it would instantly have 100M+ users. That aside, with a better onboarding flow they might be able to lap Mastodon.
Breaking the walled garden would cost them. E.g wouldnt it mean allowing people to interact with twitter without using the official apps, meaning losing ad revenue? (Obviously why third-party apps were banned)
I wouldn't think Twitter was ever likely to adopt something that will allow it's users to move away and easily keep their followers.