I'm not sure what to think about the new upgraded driver to be honest. I bought the headphone used and as part of testing it I ran bass shaker tests and noticed right away that one of the drivers was rattling so I RMA'd it within a few days of owning it. I really only know what the new drivers sound like in regard to the LCDX, but I also own a pre-fazor LCD-3 that I can compare it to. The LCD3 I own has a FR more in line with your old LCDX which to my ear sounds more natural. The LCDX has a weird upper treble spike (10khz on the FR) that you can hear especially on cymbals. For example, a crash will have more emphasis on the decay instead of the initial hit of the cymbal, if that makes sense. I've seen other people describe it as "tss" or "sss". It's not a deal breaker, and barely noticeable, and not even noticeable on all songs as most songs aren't even recorded with real drums now a days anyway.
The LCD3 has more natural treble, yet its more rolled so I feel like Audeze tried to bring more treble to their headphones by spiking the 10khz which brings an unnaturalness to it- I believe this is what you mean by the whole LCD4 and Tyll thing. I haven't heard the LCD4 yet, but its by biggest fear as I want to upgrade to it, but if it still has the same problem I'd rather stick to my LCD3.
The newer drivers supposedly bring bass back to the Fazor headphones, and are also, supposedly, less failure prone- so that in itself should be worth it despite the weird treble.
Here is my LCD3 (prefazor) FR for comparison purposes: