Liking what I'm seeing so far, had a lengthy post of praise and suggestions that I accidentally canceled.
I'd had similar ideas but the class was more a cross between engineering and warlock than engineering and hunter or engineering and shaman, though now that I look back on it all three would be viable.
Start with a nondescript-ish tinkered thing that provides extra lowbie DPS and functions as a turret. At Level 10, the spec choice is the first 'upgrade' - Mech Suit for tanking, spider-tank for ranged DPS, or broken down into multiple mini-bots for the buff/mez/dps variant. Mech suit could have features from found weapons and armors integrated, destroying the armor but adding it to some stat-allocatable resource (call it salvage?) to make permanent changes. Same would apply for the ranged DPS class, with one possible talent option being the choice between being a rapid-fire gatling type or more of a heavy-firing bombard capable of using explosives from engineering as ammo to increase base skill power, as well as giving the excuse to bring back ammo for engineers as a consumable 'buff' rather than a limited resource (stack of basic copper shot gives a slight temp buff until ammo is depleted in say ten minutes, while thorium shells give a bigger one at level). Thrid spec would be more like a melee and bomb thrower, using the mini-bots as a resource to root targets, do damage, silence areas with noise cancelling, and generally be a mezzing nuisance in PVP and in fights where certain mechanics would need to be rapidly cancelled. The understated bonus of course is that tinker types work well together, and the melee swings of the third spec would heal friendly mechanicals - including mechsuits and spidertanks of other tinkers as well as their own minibots. In a sense they'd be the RTS class setting up impromptu strategies to best utilize their constructs for victory, including transforming some of their minions into temporary buff-gear for allies. Rocket boosts for tanks! Reflex overclockers for DPS! Magic amplifier-batteries for healers! Of course, with each minibot spent in such a fashion, that's one less for the tinker to use for their own DPS, but thems the trade-offs. Good thing you can make bombs, right?
To go with this, all crafting professions would gain craftable items in their repertoire that the tinker can use for permanent upgrades to their mechs - comfy lining for cloth, panel decals for inscription, reinforcement plates for blacksmithing, keep patches usable on mechs for leatherworking, socketable gems remaining viable for jewelcrafting. Goblin rocket fuel becomes a hot demand resource for self-cast buffs. The third tinker spec, I'm not sure what improvements they should get, but being able to heal mechanicals and buff/mezz is pretty much something I see people not 'getting'. Ah well
TL;DR tinkers as a class should have the equivalency of a built-in heirloom that fills the role of what becomes their class specialization.