Yes, some people are quite vocal with their expectations... and most interestingly some of them consider Beyerdynamic (in this case) staff complete idiots that have no clue what they're doing. Which is absolutely not the case... I know many people there for years, and I think they are actually reflecting very much on their past products, what might be interesting to their customers. And changing something that many consider the Beyer housesound does require quite some courage I think... Keeping such an old company so agile that they don't simply continue to do what worked in the past, but try to evolve, get better in relation to what is now, not what was yesterday -- I think that's a good thing.
I'm really interested in trying the new T1 myself (I just can't stand midbass, so I'd rather start with the T1). Interestingly I was always on the brighter side of things (headphones that is), but came to appreciate a warmer signature over the years. Overall I think what the founder of Lake People once said to me is true: "If you actually listen to a concert, it is just not as bright as some want to make you believe. Natural sound is much warmer." Treble is to a certain degree an effect, a bit like bass: you suggest details and room, where you might have to listen much closer to actually hear it with a natural presentation. Overall that natural presentation is much less fatiguing though, since our brain does not analyze details and correct/eq so much, but can more get into the music I'd say.
And I'm sure neither the T1 nor T5 are actually missing details. They are just not in your face. Coming directly from a bright headphone they might sound dark, but with the direct comparison fading I expect them to sound very natural actually. As I said: I'll have to try