If tinkers for shields were added, presumably there would be both defensive- and offensive-oriented tinkers? This could get complicated: since one can block with a steamsaw, might they be able to use shield tinkers in addition to weapon tinkers? Should shields be allowed to use weapon tinkers? (Stone warden, I'm looking at you here...)
The idea of mainhand/offhand tinkers, rather than weapon and shield, briefly occurred to me, but that doesn't make a whole lot of sense lore-wise, as all the EoR classes are dual wielders.
Of course, this brings up the idea of a very tanky steam-using class, and the addition of a Steam Powered Shield to the set of steam powered fixedarts. Though that raises its own problem completing the set for most classes.

...and seeing as Mana Coil is already a thing, why not a steamcaster class, if we're going there?
Any thoughts?