The elementalist would be a neat additional class, but I think I liked the old mage class better, so I'm not too happy about losing it. For one thing, it's not great having every single mage more or less pigeon-holed into a single element; playstyle issues aside, it's rather limiting to character concepts.
In fact, I'd go a bit further and say that the new class reworks are part of a troubling trend to reduce the flexibility of the character classes. The changes to the ritualist class are an even stronger example: in the current (live) version, you can build your ritualist as a priest, a necromancer, or a druid, or some combination of the three. The new ritualist class seems more or less locked into the druid concept.
I really liked the flexibility of the original system, but the rework at least fleshed out the classes enough that you could develop a theme more fully than you could in the original version. If you wanted to build a fire mage, you could do that. If you wanted to build a tri-elementalist, you could do that as well, although you'd have to make some tough choices to do it. In the beta version, if I want to build a fire/lightning mage? Tough, that's not allowed any more; you just have to pick one element. If I want to build a dark priest, combining healing and necromancy? Tough, your ritualists are all druids now.
The beta seems like a strict downgrade in terms of the ability to create the hero archetypes that I'd like to create. Which is ironic, because the ability to choose tome paths for custom empires is a massive improvement to the ability to create the empire archetypes I'd like to create.