So I thought it may be fun to create some new full-fledged original classes for B&T. However, I was thinking of making them slightly different.
What Heroes of Lore did is take the basic theme of a class and modify it slightly. In fact, many classes could probably fall under this sway: wardens are druid variants, tattoo mages are sorcerer variants and so on. Variants are easy to make and not extremely "special."
However, I feel new classes are needed if you are introducing entirely new mechanics. My summoner variant probably should have been a new class, but I think it's good enough to stand on its own. There are two classes I think would be great for B&T, even though they would be very setting specific: the Spellblade and the Gadgeteer.
I said in my 4e in B&T post that the Warlock variant is basically the spellblade, but this is missing the main point of a spellblade: their ability to charge their weapons with arcane energy. I think that's distinct enough to constitute its own class. An easy variant would be the Gun Mage, who channels his powers through a gun rather than a sword.
Gadgeteers will be interesting in that they will more fall along the Sorcerer path in that they will have variant castings. Their powers will instead be in gadgets that they can use. I'm also thinking of giving them the ability to build clockwork constructs. This class would be good for high technology campaigns. A variant could be steam augmentation to Gadgeteer's body