I saw the same tweet and I signed up for the beta because I was curious to get on the Things 4 beta train.
Since then, I am beta-testing Things 3 on all three platforms… 
So, no, that tweet does not necessarily indicate Things 4 being on the horizon. Apparently, they just wanted to have more beta testers for Things 3. Then again, I think that we might hear about Things 4 within the next 12 months (without knowing anything myself, just guessing).
My strong opinion is that Cultured Code considers Things to be feature complete. We will see platform updates and small features here and there, but no big new features. I guess it’s probably ok and if that’s the case CC can keep operating like it is currently doing without going to a subscription model. Charging head on against subscription based apps would alienate their user base and I guess they don’t have the team scale to pull that off.
Edit: the risk of this strategy is that native Reminders capabilities are only going to get better and better so the value proposal of Things becomes much harder to sell: it’s not obvious that the best feature of Things is not the beauty of it, it’s the opinionated workflow that enables you to follow.
It’s actually quite difficult to realise the value of Things without using it for extended period of time. On the spec sheet it’s not that impressive. But the fluidity of the whole experience feels like the most valuable in a task manager for me. Every now and then when I try to drift away from Things and try out its competitors with better feature sets, I almost always give up in the first 20 minutes. I’m clearly biased and spoiled. But if I don’t enjoy the experience of the task manager, I’m just not going to open it at all when it’s filled with a bunch of headache-inducing tasks.
Totally agree, the flow of Things is not obvious beyond how beautiful it is. Using Things just as a “more beautiful Reminders” you are missing out.
The only thing I find missing in Things is 2-way calendar integration, but I do not expect that to happen: the Things Doctrine does not include time blocking.
Drafts app has an action for parsing a list into things as a project
Works flawlessly and I have moved all my things templates to drafts now
That and the fluidity of doing everything function in Things. This app is buttery like no other!
Exactly this. To be honest, I think I’d prefer a subscription model for the next release. At least we might see regular feature updates and better response to user feedback. I live in this app everyday and nothing comes close to its user experience on iPad with the magic keyboard. But I do find my eyes wandering to apps like TickTick on occasion, as I see worthwhile features being added on a fairly regular basis.
Of all the key apps I use, Things is the only one where I literally have no idea where the product is going or what might be around the corner.
Rant over. My apologies 
I would like to think that was the case but if Text Expander is any indication, that is far from certain.
Attachments, Attachments, Attachments. I want Things to act as a project hub where I can park things, complete the task/project and then archive/delete. This would be a game changer. It would also be nice to be able block schedule in Things and have it appear in Calendar or Fantatical.
Siri integration would be nice.
Bud
Siri already works with Things.
These aren’t really predictions, since I’ve kind of given up on Cultured Code ever doing them, but I’d love to see adjustable text sizes on both their iOS and macOS apps, a review function, and better management of repeating tasks (or at least the ability to complete them early).
I don’t know what to say about pricing. I don’t think that I’d pay for another full set of apps up front given the leisurely pace of improvements. I also don’t feel that I got anything approaching good value out of the Things 2 to Things 3 transition. Removing text size adjustability, in particular, in the move from 2 to 3 on macOS was a big usability step backwards for me.
Stranger… Things 4 is already out.
It’s not a prediction, it’s a wishlist
In the column for evidence that Things 4 will not soon materialize, the Status Board on Cultured Code’s site has it’s first forward-looking status update in a long, long time: Annual newOS Support, in Development for This Fall.
In looking for something else, I ran across this from PCMag:
"When Will Things 4 Come Out?
This to-do app has had the name Things 3 for years, leaving many wondering when will there be a Things 4? I reached out to Cultured Code with this question. A representative replied that the team has no plans to announce a new version and that Things 3 continues to receive full support and ongoing updates.In short: Things 3 is the app for now and there’s no plan to release Things 4.
Source: Things 3 Review | PCMag
If accurate, that is not a good sign for the future development of Things 4. Given advances in other task managers, Things 3 is getting dated (though the UI is nearly timeless) having been released in 2017.
That’s disappointing.
Maybe I’m just being optimistic, but I take it as “we aren’t ready to announce Things 4 yet”.
I don’t know that I’d read too much into that. That sounds like very Apple-like PR speak. Many developers are understandably loath to comment on upcoming releases until they’re ready. They probably don’t have plans to announce a new version, because it’s not yet ready. But that could change in a week, a month, or a year, once they feel its ready.
Is Cultured Code a full-time development shop? It doesn’t matter to me whether they call it Things 3, Things 4, or Things X. It’s the pace of development/features that’s frustrating. Hard to imagine they can sustain a business like this, but what do I know. I’m fully expecting to be disappointed again by this year’s updates, which we’ll undoubtedly see next week for iPhone and October for iPad/macOS.
It is interesting in that I miss two things in Things and one thing in OF (that’s a lot of things! My writing teachers would be horrified.)
In Things, I miss the “when” date and the quick entry feature.
In OF, I miss the review feature.
But, for my needs, I gain more with deep system integration with Reminders than I lose not having those features. I’m also growing more “dependent” on the smart lists and tagging features in Reminders, which I find constantly helpful.