DTA lite (web extension version) was planned for release along with Quantum, but was delayed. [1] I still don't know how limited it will be compared to the XUL version though.
He was the only bigger extension dev that threw a complete tantrum over this decision, refusing to even try to work with Mozilla to get some APIs into place, so that he could maybe actually port his extension in full. And now he's doing a port anyways.
Well, good on him. I do not think that his behaviour back then was entirely justified, so this remedies that.