People know that "class" was never really a part of TES in more than name, right? The "classes" you can select are just skill templates. Your character has always been created by selecting which skills you want to use as primary, meaning you start with them being higher than others, and you level up (i.e. increase attributes and gain health and mana points) when enough of those skills are raised.
Skills have always been the name of the game. And being able to mix and match any different skills has always been the name of the game. If you wanted to be a heavy-armor wearing mage who hits things with a massive, heavy sword you always could.
The question isn't, are classes all going to become like each other. The question is, are skills going to be mashed together, and the number of chosen skills reduced, to the point where any character can easily become good at all of them? In Morrowind if you didn't start with a certain skill, it was hard, and took a LOT of in-game time, to get that skill up to where it was usable (unless you abused trainers). It's possible, though, that what with the number of skills going down from whatever it was in Daggerfall, to 27 in Morrowind, to now 18, that it is becoming more and more difficult for characters to differentiate from each other.
I still think the number and type of skills in Daggerfall was the best option though (except the entirely worthless language skills). If you don't know, you got to pick from a very large pool of skills, most of them quite specific. What became Athletics and Acrobatics in Morrowind was originally Running, Jumping, Swimming, Climbing and maybe some others. Dodging was removed and became, I think, a side effect of Agility. Lock picking and pickpocketing were separate. Speechcraft was divided into skills for speaking to all different levels of society. And so on. You could pick three primary skills, three major skills, and five minor skills. In MW of course, they reduced it to 27 skills with the goal that each skill should be useful enough for some character to make it a major skill, and you got to pick five major and five minor. In Oblivion they knocked it down to 21 skills and you just got to pick 7 major ones. Now we've got 18 skills and I'm not sure how many you pick.
Anyway, what was cool about Daggerfall is it allowed characters to be way more differentiated and specialized. Sure, not every skill was good enough that you'd want to use it as a major skill, but who cares? Nobody is going to role-play an Olympic swimmer, but it's cool that you can have your character be above average in swimming. Or climbing or whatever.
Daggerfall's "perk" system was also cooler, I think. In Morrowind and Oblivion you got to pick a birthsign that gave you certain advantages (and sometimes disadvantages) and/or activated abilities. They were pretty unbalanced in Morrowind, but less so in Oblivion. But in Daggerfall you could pick from a long list of handicaps and bonuses, each worth a certain value, and if that value was around zero, the speed at which you levelled up was normal, but if it was higher or lower, you'd level up faster or slower than average. You could pick all kinds of different stuff, like only being able to use magic in daylight or at night, or regaining health when submersed in water, or I can't even remember what else. Once again, a lot of them were broken (99% of fights that mattered happened in dungeons, so being unable to use magic in daylight was almost a free way to be able to afford other bonuses), but the point was there was a ton of customization available. That gets lost the more you "streamline."