The question is, which aspect is monetized: reading or writing? If it's reading, then I see Twitter quickly losing out to a platform that is free to read. Politicians and celebrities wouldn't make announcements on a platform that requires payment to read. If it's writing / having an account, then the suggestion is a lot more reasonable. I would pay $4/mo, and would be very glad to not have spam comments below every tweet I read.
Twitter is a first-responder medium. If people had to pay we'd miss so many breaking events that make it valuable to journalists et al in the first place. That model would work for a newsletter , but not for a live medium
It enhances the experience on Twitter for those that desire more features: a thread feature (which is /really/ nice IMHO), ability to cancel tweets after send, more color themes and customizable icons, etc.
The Twitter "as we know it" will likely always remain free and ad-driven, but if you want an enhanced experience, you're going to have to pay for it. And that's fine by me.
I'd buy twitter blue right now if it didn't still have ads. I'd pay 3 times its cost if it was just ad free. Sure it's not a problem on my computer because I have adblock but I primarily use twitter on my phone, and I'm too lazy to set up an adblocking DNS like pihole.
A carefully-applied monetisation model could be quite helpful for the community as well as Twitter's bottom line. Private accounts - perhaps with an extended network, friends-of-friends - could still remain free and generate ad revenue.
The one issue is that chipping off existing features would cause major backlash. While removing low-quality replies and other spam is nice, it relies on even higher-quality moderation, to provide adequate incentive not to lose out on a purchase, but also to avoid regulatory issues, as this now becomes a product.
When it comes to adding features to sweeten the deal, however, there are very few that can really be added that provide a tangible benefit. The only feature I can think of is being able to edit tweets - or more accurately, embed a second tweet, similar to a quote-tweet, to provide an update. This would allow people to provide context, retract claims, or other uses, especially when a tweet gets attention or controversy, and could go a small way in reducing toxicity.
