Unarmed was never popular in games that didn't support it. Morrowind had an unarmed skill. In Skyrim you needed to play Khajiit, get the one unique enchanted item and invest in heavy armor for an effective build. ESO doesn't have to be like that and monks/martial artists in other games seem fairly popular.
I don't see any problems that Onehand+Rune has that a tinkering skill line wouldn't. The rune is just to describe the spell in the offhand. Sure, it could be a new weapon acting as a focus, like a scroll or a special ring but it could also work with an empty offhand. There isn't even a need to make new mechanics or assets for the motifs for it.
Tinkering on the other hand, while admittedly very cool, would have to more or less completely revolve around traditional permanent pets.
Undead can be fire and forget (who cares about them), animals have their own life and can make their own choices, but automatons behave like bound Daedra in a sense. Even worse than Daedra, if you spend weeks tinkering on your spiderworker, you won't command it to commit sudoku on the enemy. It'd be your precious baby and you wouldn't risk getting it destroyed.
The problem with permanent pets is that they are really nasty to deal with in pvp. They provide cover, they provide effects like healing that don't go away unless you focus them and not your actual target etc. If the game could handle more permanent pets, then Warden and Necro would have had them. Fire and forget doesn't sound very plausible for a tinkerer unless you are talking about bombs.
Maybe as a weapon skill line and not a guild. Think of a dwemer control rod that could look like a smaller 1h version of a staff (but counts as twohanded or something). It would be better because you wouldn't have to worry about getting destroyed by destro ults while dealing with the pets it summons. They would either work like the Skeletal mage/archer and Spirit mender or as one pet that your spells give different commands to, to not be too cancerous.
It's a fresh idea and I like it a lot, just not as much as I would like to play as a Spellblade archetype with 1h+rune.
Until then I guess you can use the stuff from the Dwarven crown crates and decorate your house with pipes and and cogs and the numerous spider pets and mounts while wearing apostle style gear.