Are you saying that alkaloids are the only substances that can cause intoxication of some sort? If that's the case...its organic chemistry time for you.
If someone would like to correct me on this with the name of a narcotic (which, unless it's an opiate/opioid isn't a REAL narcotic using the definition)
Nope. A 'narcotic' is any substance, regardless of if it is synthetic or naturally occuring, as long as it produces the same types of effects as opium derivatives. Methadone is a synthetic molecule that produces the same types of effects as opium derivaties, but as it is synthetic, is not an opiate. Really the molecule just needs a phenyl ring directly attached to an sp3 hybridized carbon that is connected by a bridge to a nitrogen atom, which must be 2 carbons away from said sp3 carbon.
Coniine, and that's more of a neurotoxin (if you REALLY want to split hairs!)
Split hairs about what? Coniine is a neurotoxin, plain and simple. If someone is calling it an intoxicant/narcotic, that's wrong. Though it could possibly have some sort of the same effects in incredibly small doses, that does not classify it as anything but a neurotoxin based on other factors.
S. flava liqueur is probably a bad idea
In large quantities, yes. To give it a taste, I highly highly doubt it. Coniine is toxic at about 0.18 grams. I think you would have trouble finding a flava with over 0.18g of coniine present at any time, as it makes up a compartively small amount of the total nectar. In fact you would need to ingest at probably
at least 20g of nectar to even potentially be in danger, which would require you to lick many a lid, as I can't imagine even a mature flava has more than 2g of nectar present at any given time, and that's pushing it.