Well I don't really see a point in making a new skill just so that people can make traps when they already have magical traps. And this may just be me but in all of my assassin type characters, they had at least a decent magic ability.
I see your point but this contradict 2 features:
Pure class Bethesda is "as they say" trying to achieve by limiting broader chaotic skill expansion
Class ressources, if this is nt implemented everybody will be a mage-something or a something-mage, and its clear in the Lore that not everybody is able to be a mage or have mage like habilities.
So maybe not bombs, but to be able to craft and lay traps would be an awesome feature with diferent effects trought alchemy would br awesome.
In fact i m agaisnt bomb like things this is too ninja earthly oriented feature and TES hold no Oriental inclined civilization that we know.