What exactly is it that people don't think fits with Eberron? I've been following Eberron since the first book came out, and I get that guns aren't an assumed thing, but there's nothing saying that the thunder cannon (or whatever it's called) of the artificer isn't a special, rare thing that was invented only a few years ago and hasn't caught on. It's not common enough to be a ubiquitous part of the setting, but it still exists.
Speaking only for myself (which seems appropriate), I think there are two major, but related, objections I have.
1) I don't like guns in D&D (in its role as default fantasy RPG), as a rule. There was a thread on this, not too long ago, where I conceded that I could imagine where someone could conceive of settings that would mix guns into fantasy in a way that worked (urban fantasy, obviously, and things like Deadlands or Shadowrun). So far, no one has done it in D&D, but that doesn't mean it couldn't be done. From this perspective, I'm unlikely to ever be a fan of
any class, regardless of name, that pretty much boils down to a gunslinger, assault gunner, or anything of the sort -- especially if it's positioned as being "vanilla" D&D. Straight up, IMO, "vanilla" D&D/fantasy, by definition, excludes guns or anything that fills that niche for most purposes. If you want a "gunslinger" class on DMs Guild, great. Ditto for something setting-specific. Not so much for a class presented as universal.
2) I do like Eberron. If Eberron is viewed through a lens of being steampunk or some such, that seems totally out of sync with #1. But, Eberron really isn't that setting. It's not just stripping the gears off tech and replacing them with glowing crystals. When taken to its logical conclusion (magic evolved instead of tech), there will be some overlap -- of course there will. But... Saying that a "gunner" subclass is totally in line with the themes of Eberron, is off the mark and runs the risk of revising the feel of the setting, especially since the Artificer class has been so iconic of Eberron since the setting was released. Does it make sense that there's probably some Cannith fanatic, somewhere, who carries around a staff with a 6 inch barrel? Yeah, probably. Does it make sense that it's one of the core builds for the class? Not so much.
To move from the "complaining" side to the the "offering solutions" side of the conversation, here's what I'd like to see:
Hang the Artificer on the Warlock chassis (with Int as casting ability). Instead of the Incantations mechanic, grant them a list of Infusions. This is in line with the idea that the Artificer isn't about raw spell-casting power, but is about taking magic and making it more available and applicable. It has the added benefit or reusing the Warlock skeleton to make it less of a one-off oddity. Break down the sub-classes as follows (names may need work). Note that I've not put this together, formally, so I'm not trying to balance, just give thematic builds.
* Alchemist -- Potion master, including oils, salves, and even scrolls. Focus on effects that are traditionally transitive, instant, or affect individuals, but that could also be used with some preparation. Ideas are things like an infusion that lets the alchemist spend a spell slot of a given level to create a specific potion (or one of a tight group) in exchange for a spell slot. The potion only lasts until the next short rest, but the alchemist could opt to renew it. Depending on balance and play-testing, I could see just allowing the alchemist to create a certain number of potions every day that would last all day (or multiple days), but I haven't fleshed this out enough to say what the balance point is.
* Maker (hate this name, but don't have a better one) -- Focus on creating what would generally be seen as "permanent" items -- swords, armor, wondrous items, etc. Infusions would have a lot to do with creating or transferring effects along those lines. For example, expend a 1st level spell slot to make a weapon, shield, or suit of armor have a +1 bonus until you take a short rest (can be renewed at that time, 3rd level slot makes +2, 5th level slot is +3). Other infusions could add elemental effects or resistances to items. Flavor is that this is the "adventuring" version of the maker, so they might be capable of doing full item creation, but the powers in play represent "good enough" enchantments that get the job done without huge time investments and remain somewhat flexible. If the source book included more formal item creation rules, I could see these guys also getting a break on time or money, or some other break. Probably better armor and weapon proficiency, too.
* Animator -- Focus on golems, clockwork creatures, and the like. This is the pet master. Pick a type of appropriate pet and get infusions that enhance it and/or your bond with it (shared casting, for example). I'm not a huge fan of pets, but it's definitely a niche that makes a lot of sense for the artificer.
* Channeller -- Master of rods, staves, wands, etc. This would be the closest to a "gunner" that I'd include. They'd get infusions that would let them maximize or modify the effects of magical devices. In some cases, this would be a lot like Sorcerer metamagic -- increased damage, better range, twinning. I could also see infusions that allowed them to just embed a spell in a stick of wood to use their other infusions on it or use spell slots to recharge a device. Some of the gunner abilities could probably be saved, but the flavor would need to be fixed.
Obviously, some of this overlaps with the previous UA version of the Artificer. I think a lot of it was just flavor. The potion master subclass just felt too much like the Skylander character who ran around throwing random crap. The Thunder Cannon was too science-y, even if not unbalanced or could be reskinned as a staff. I didn't like granting a pet to every Artificer, even though I agree it's a valid archetype it's not inherent to the larger concept. I also didn't like that the base class used the 1/3 spell progression that is otherwise reserved for sub-classes. Base classes should be either full (Wizard) or half (Paladin) casters. Warlock isn't really one of those, but it has its own internal consistency and it would also make sense that the Artificer would have a hard time multi-classing with standard casters.