Okay I misread this on your first post. I thought you were talking about DFG, not DFT. Sorry I'm an idiot.
With that out of the way, I'm torn about the return of DFT. I think it was really good, but actually, it does kind of have a similar problem as DFG, just for different champs. If DFT is good on you, you have to take it, more or less. It doesn't do a good job at helping increase diversity and player choice.
For that reason, I don't necessarily want to see it return. Aery has some use for DoT mages, and Comet can reduce CD with DoT effects, I think. So perhaps the proper way to address the issue is to simply buff the DoT champs that need buffs and leave it at that.
I'm really liking Arcane Comet on Swain, for instance, and many of the other Swain players I've talked to use other things. That's good, because it allows us the customization that was always supposed to be possible with the pre-game systems. So while, yes, DFT was fun in its own way, it didn't actually achieve the goals set out for Runes.