I think it is better than adding bicycle_parking=planter, =planter_with_wall_loops, =bilboard, =bilboard_with_wall_loops etc for every new combination (especially as =planter is not making clear that it is stand combined with a planter rather than wheelbender combined with a planter)
If you, or somebody else could make a picture of such ‘plantlock’, and then upload it to Wikimedia Commons, then, that picture is ‘free’ (of licenses) to put it then on Key:bicycle_parking page, with comment(description) , so that it can be used …
Not very ambiguous at all. Planter as a person is fairly outmoded in English now as it was principally used in colonial times. We don’t map people.
We don’t map movable machinery either.
Pretty much the common term which people use for these things in spoken English is planter. A plant container is not ambiguous either it might be anything from a flower pot to a standard industrial intermodal container (https://en.wikipedia.org/wiki/Intermodal_container) containing machinery (“plant”) (which come to think of it I can think of several locations where such things exist, although I hasten to add I wouldn’t use such tags).
Probably more importantly planter already has more widespread usage on OSM (as both barrier=planter, man_made=planter & planter_box).
‘many’ mappers are like a ‘herd’, just ‘following’ what ‘some’ have decided … and sometimes those ‘some’ were wrong(in the past) in what should be the ‘correct’ tagging of something … it is like a ‘snowball-effect’ … therefore, i made a topic about ‘suggestions’ what a ‘thing’ should best be named/tagged … maybe such topic could have a ‘sticky’ here on ‘general chat’ or something ?