To be blunt; the amount of effort required to make something -reasonable- would *far* outweigh the benefits for a *space* game.
People seriously underestimate the amount of effort required. Even something like NMS which has already been derided in this very thread as not even trying to be plausible took *years* to achieve what it has managed to create. NMS arguably has a smaller dev team, however, that is the *core* selling point for their game which explains the amount of effort they put into this aspect of it, to the detriment of other aspects (eg flight model).
In Elite, plants on planets would be a tiny niche, very briefly explored by the masses before they go back to their pew-pew or trading, and explored in depth (and complained about) by a few interested people.
And this is without even trying to get interactivity into it.
And finally I have to ask: what actual *gameplay* would this bring to *Elite*? In NMS, it's core gameplay to discover, tag, and name new animals and plants. Do you want the same in Elite? Or is it just for pretty backgrounds?
Before the latest patch, we didn't have a way to map a planet's surface, now we do. This added another aspect of gameplay to the game that wasn't there before. How is this any different from having landable atmo planets with things for you to map and discover? It starts to get more NMS sounding, but it's seems to be the next logical step.