It was already confirmed the next device from OnePlus will launch in the second quarter.
So, probably we'll have it around June. If you can wait,...
OnePlus 5T will not have Project Treble.
You can read the official statement in the AMA done here in the forums.
The new functionality is only available on the Open Beta 3 so far.
If you have the money, yeah, the 5T is a good phone. The camera could be better.
The 6 should be released around June, 2018, if it's like the 3 and...