I have to imagine that a free Lemmy version of most communities would be more appealing to most people the paywalled subreddit. But I also have a feeling the paywalled subreddits are going to be crypto or meme stock related, where there's a benefit to them being paywalled.
EDIT: As other have said, there's an incentive for the porno subs to be paywalled too.
That and Crypto/wallstreetbets is what I assume. But like most subscription services, the paid tier will start out as "bonus" content but eventually more features get locked behind the paywall.
If they're foolish enough to paywall old.reddit it would force a lot of the olds out.
This is just the next logical step towards locking the NSFW communities behind a paywall. But, I don't think it's for the revenue, mostly. It's an essential step in tidying up their image and dealing with the regulations around internet censorship and linking real identities to users. They'll make way more money off of marketing to and marketing data of a fully identified userbase. They've already profiled them, linking those profiles to real people will just multiply the value of those profiles. Reddit is Facebooking themselves, selling out their users to turn community into a product. I guess since nobody google searches anymore, and Google did the same thing, we could also call it Googling themselves.