Unlike always, I'd be direct: Should we merge lewis-structures and the newly renamed structural-formula because Lewis structures are clearly structural formulas and the Wikipedia page for "structural formulas" says I'm right in saying that and no matter how much high schools love Lewis structures and how many questions we get from them and how much unpopular Newman or Fischer projections or others are at least in elementary courses of organic chemistry they're still a clear subset of structural-formulas and keeping the tag would make no sense because someone who wants to tag their question as lewis-structures could tag it as structural-formula legitimately and if we merge them they could get to tag their question as structural-formula even ignoring the fact that Lewis structures are structural formulas by simply typing "Lewis" in the tag box?
- lewis-structure is more specific. There are structural formulae that aren’t Lewis structures.
- lewis-structure is probably (although I didn’t check the numbers) a tag of it’s own right.
- lewis-structure definitely includes electrons in the structure while structural-formula — or worse, skeletal-formula — usually don’t.
- Since Lewis structures are usually used in high school or the very first year of chemistry, a lewis-structures would often attract different questions and require different answers than those structural-formula.
If Stack Exchange decides to implement a tag tree rather than a tag list one day™ (didn’t someone want to make a meta.SE proposal?) then yes, have lewis-structure as a sub-tag of structural-formula but let’s not put them together just like that.
(On that note, I would not oppose stereochemical-projection for Haworth, Newman, Fischer or sawhorse projections for similar reasons as highlighted above.)
I know that this answer is not really well written and all of the reasons more or less boil down to one. But I really don’t think it hurts to keep them separate and it might hurt if we want to separate them in two years.