Well, it all depends on how you picture a shaman, right? I think focusing a shaman on binding spirits into totems or fetishes could make an excellent way to use a hypothetical "imbuing" mechanic class in a nature/spirit/primal oriented direction. I'm seeing some combination of Warcraft Shaman, Diablo Witch Doctors, and the Werewolf rituals from World of Darkness as a good inspiration.
So you have a class with a new novel mechanic for tying spells into items, and then the Shaman uses the Druid spell list as his baseline, the Alchemist uses Cleric (alchemy potions focus on healing and granting new abilities to the drinker), and Alchemist uses Sorcerer or Wizard (and focuses on making blasting items, as well as cloaks of invisibility and such tools.) I think a mechanic where the item itself can maintain concentration on a spell, but the user can only benefit from one imbued item at a time, would be an interesting mechanical niche to explore for such a class.
I see it..what you and Mr. Mearls are talking about. I DO! I'm just not sure it is the best way to go about it.
Inherent to the class/subclass structure is that there needs be some commonality of flavor, story...raison d'etre, that is part of the
class...and so "trickles down", if you will, to the
subclasses. No matter what circle you choose, you are a Druid. No matter what style of warrior you are, you are a Fighter. No matter where your specialities lie, you are a Rogue.
Taking two "science-y" -implying civilization, advancement of knowledge, technologies- classes and lumping them in with another subclass that is, by definition...or at least immediate word-association, conjuring images, and game legacy [from 1e on with the monstrous humanoid shamans/witchdoctors of the DMG] of "primitive" communities/peoples...a more [to borrow the 4e nomenclature, but note the small "p"]
primal mode of magic-working/spell-casting...
Lumping them together under "No matter what kind of spell you imbue in what kind of item, you're all the same class" just isn't...I don't know...it's not "enough" for me. OR perhaps it is too vague to constitute the flavor/story of other classes. It's not a strong enough coherent flavor for the Class...though works/is justifiable if you tilt you head and squint for the subclass.
Take the Artificer and the Alchemist and make a class. Absolutely! My half-hearted rewrite of the UA artificer lumped alchemist in as a subclass (and something I just called a "Golemancer" for the makes other mecha-magical creatures/things type)! Rangers & Barbarians & Bards are all "base classes" with only 2 subclasses each. The "technological/sciencey guys" can be subclasses of their own class without wrapping in shaman, very handily...all imho, of course.