I don't think anyone saw this coming!
I'm unconvinced. For low-magic campaigns, this class is problematic, and given the power curve in 5e, I see a lot of campaigns going low-magic.
I have what I consider to be an ingenious, nay brilliant, conception for a solution to this most heinous of problematicisms!
Don't allow it in a low magic campaign.
Now this is an artificer I can get behind! (Because I wouldn't want to be in front of her when she's throwing alchemist's fire all over the place - hah!)
I like it. It's not quite what I would have done, but this has more of its own identity (mine was more of a reskinned Bard). On the first read-through, there are three things I'd add:
1. This is highly campaign-dependent (based on how much item creation the DM allows, so maybe there should be a sidebar about it), but the core identity of the 3e artificer was creating and use of magic items. They had the ability to use the skill Use Magic Device to bypass item creation requirements, primarily that of spellcasting. For example, if you wanted to make a pair of boots of the winterlands, you needed cat's grace, endure elements, and pass without trace. But the artificer had a very good chance of making them anyway. To reflect this ability in 5e, I would put in something like this:
Arcane Polyglot: The artificer is a master of using and crafting a diverse array of magic items. An artificer ignores any requirements on attuning to a magic item. If the campaign allows for PCs crafting their own magic items, an artificer would be able to bypass any spell knowledge requirement on the item, as long as the artificer's level is at least twice as high as the spell level. Example: In his campaign, Staffan has decided that in order to craft a Staff of the Woodlands you need to use the heartwood of the oldest tree in a major forest, with the permission of a treant native to the area. You would also need inlays from a certain number of rare trees, placed in a precise pattern portraying various animals. You also need to expend a few thousand gp worth of other components, and cast a number of spells including wall of thorns each day of the crafting. Nikolaj is playing an artificer in Staffan's campaign - he needs to buy/make all the stuff, and spend the time, but he does not need to cast any spells, and once the staff is finished he can attune to it even though he's not a druid.
2. I'm not too fond of the limited spells known for an artificer. Having full access to their whole, albeit rather limited in focus, spell list was one of the cool things about them in 3e.
3. There needs to be a clarification on how Concentration works regarding Infuse Item. I would have the item's user be the one concentrating on the spell (which would enhance the artificer's role as a buff specialist), but I could see it either way, and it needs to be clarified.
It might not give cantrips per se, but the Satchel and Thunder Cannon serve the same purpose.
I'm inclined to run low-magic (item) campaigns, so probably wouldn't use the Artificer, so can't really contribute much.
But, I do find it odd, after all the hand-wringing over and reluctance to introduce missing full classes, to see one put forth for a fairly specific and Ebberon-originated concept ('Gunsmith' seems to put it in that sort of fantasy-steampunk milieu, too). Maybe Eberon's in the offing?
Or might it be used as a foundation for a wider range of sub-classes. (I seem to recall Shaman as Artificer sub-class mentioned.)