Which was basically reflavored spellcasting with a spell point system.
No, it isn't.
When you use psionics in 2nd edition, you roll an ability check. That's a big difference, and it represents a specific narrative difference between magic and psionics.
Also, access to most of the powers is not limited by level. Instead, you get better and better at them, which is called psionic "mastery" in earlier editions. I think that these two features are at least as defining of psionics as the point system. And all three of them have narrative relevance.
Also, completely overpowered
Yes, and that's why 3rd edition and later distorted psionics for the sake of uniformity. But I think that 5E is a very solid and flexible system, and it can do better than that.
There is already an optional spell point system if the DM wishes to use it.
Yes, and warlock or sorcerer can be reskinned and modified to serve as psionic classes. And if there will be an UA article about that, I think there's nothing wrong with that. That's completely in the spirit of 5E. That's something that 5E was designed to be really good at.
But in Dark Sun, psionics is fundamental. More so than magic. If you want psionics for Dark Sun, then what you want from psionics may be different from a campaign where psionics is marginal. You may want magic to be mechanically distinct from psionics, because in Dark Sun it's really important about magic that it's not psionics.
So I'd like if they published some ideas about building a more peculiar kind of psionics too.