The fictional plants just need a little love, IMHO.
The above quote is mostly about the "McNugget" like feel they have, which is mostly caused by their not having been refined and purified as ideas.
Natural plants have this refinement built in-- Things like the mythological silliness behind mandrake roots, et al.
Toady is busy bashing his brains in on logic problems, loop execution optimisations, bug hunting, etc. All too often, this precludes taking time to sit and daydream about fantastical components of his game.
I suspect that it is this time constraint issue in regard to spending the time to refine the fantastical elements into beautifully complex abstractions on which "cultural" things can hang that is the real motivator for him to scrap them.
Personally, I think things like plump helmets, sunberries, and such already HAVE cultural significance--- They have significance here in our forum community. We have each tried to envision these plants as best we could from the limited information available, and a wealth of community stories have been crafted, (of various levels of quality, which I wont elaborate on) which when taken together, could be used to flesh out these crops, if one were to take the time to do so.
At the end of the day though, it is toady at the wheel. If toady decides to axe sunberries and pals, I fully expect the mod community to do the fleshing, just because of this community cultural growth those crops have produced.
There aren't that many of these "original plants", after all. The new raw structure has been (mostly) finalized for herbaceous plants. Some real-world biome evaluation for plant morphology and some inventiveness, and we can have a new-raws compliant "original plants" mod. Probably a great many to pick from.
Who knows, if the community distilled versions are of good enough quality, toady might decide to incorporate them. Again, I think the real issue is the time and energy needed for that distillation and refinement.
I don't think time constraints have much to do with it really. It's fairly obvious looking at Toady's approach to much of the game as well as his answers in the DFtalks etc that he has a really big thing for procedurally generated content and much prefer that over premade stock fantasy. While there has to be some stock features to help ground the whole thing and not make it all a big confusing random mess I'd say a good balance has been struck so far at least.
The underground plants at least seems to sit fairly safe, as they should, and they're really the ones with most of any cultural value so far. Sun berries might be attributed some sure, but the rest? They really don't add much more than an unfamiliar name. Setting up a simple system to throw in a reasonable amount of random plants to take their place, possibly with a few minor magical effects to spice them up definitely sounds like a better idea to me.