SuttaCentral
But there is nothing in the form of the compounds kāyānupassī, vedanānupassī, cittānupassī and dhammānupassī that tells us whether the first term in each compound should be taken as singular or plural.
That being so, if a translator is sold on the as (or the qua) construal, then he can simply match the number of the first item in the compound with the number of the locative-case term:
body qua body.
feelings qua feelings.
mind qua mind.
dhammas qua dhammas.
Or even she or they!
Too much education; making us doing too much google search… 
Is Qua acceptable in scrabble?
Yes, qua is a valid Scrabble word. More definitions: (conj.) In so far as; in the capacity or character of; as.
/kənˈstruː.əl/ the way a person understands the world or a particular situation: A young child’s construal of a task may be different from an older child’s or an adult’s. Understanding and comprehending. apprehend.9 Nov 2022
Each of the oblique cases in Pali occasionally conveys the sense usually associated with one of the other cases. In the grammars this is referred to with terms like catutthyattha-sattamī (“morphologically locative but semantically dative”) or catutthīchaṭṭhī (“genitive used as a dative”).
This sort of thing is especially common with the locative case. The Padarūpasiddhi (available at the VRI site) is a rich source of examples.
“The locative is extensively used instead of other cases, and the student must be prepared to meet the locative where very often he [*] would expect to find some other case.”
(Charles Duroiselle, Practical Grammar of the Pali Language)
[*] or she.
I first encountered qua when I played the role of Lucky in a school production of Samuel Beckett’s Waiting for Godot, but I didn’t realise that it actually meant anything. I thought it was just a gibberish word, like so much else in his crazy theologian speech.
The second encounter came when I read Trevor Ling’s Dīgha Nikāya anthology, The Buddha’s Philosophy of Man (1981), where he uses it in his translation of kāye kāyānupassī, etc., in DN22.
Other than Ling and I, the rendering doesn’t seem to have many takers. The only other person I’ve seen using it is Sue Hamilton in her book on the five aggregates.
Great book !
Should be better known.
I realized that but was typing on a tablet device so tried to keep it short. I apologize, I won’t do so next time!
You’re both right, of course. But then you’ll still have to explain why vedanasu is actually plural. Because when the suttas speak of understanding the aggregate of feeling, it is elsewhere always in the singular. Here it is plural, which is quite unique and therefore telling, in my eyes. It makes it more likely Ven. Sujato’s interpretation is right.
But it’s not a wild card to do whatever we desire with the cases. There are limits on these uses.
So I belief you should have a precedence for this use. And I’m not aware the locative is used that way of “as”. If so, it’s surely much rarer than the locative of “among”, which is quite common.
Assuming the above is correct, my personal explanation (speculation) is:
Dependent origination is about a moment of sense contact leading to a certain type of craving. Here, I imagine, it is expected only one type of feeling arise from a particularly sense contact; therefore singular.
Satipatthana is about four general areas of prolonged contemplation. Therefore, whether following MN 10, where both painful & pleasant can arise in a meditation session; or whether following MN 118, where both rapture & happiness can arise in a meditation session, it seems expected more than one type of feeling is experience in satipatthana; therefore plural.
Similar, with Dhamma, there are different Dhammas, such as impermanence, unpleasurableness, not-self, dispassion, nirodha, etc; therefore plural.
There is only one citta, although it may change its state or colours; therefore singular.
“This mind, mendicants, is radiant.
“Pabhassaramidaṁ, bhikkhave, cittaṁ [singular].
But it’s corrupted by passing corruptions.”
Tañca kho āgantukehi upakkilesehi upakkiliṭṭhan”ti.
“This mind, mendicants, is radiant.
“Pabhassaramidaṁ, bhikkhave, cittaṁ.
And it is freed from passing corruptions.”
Tañca kho āgantukehi upakkilesehi vippamuttan”ti.
Similarly, kaye = multi-faceted-group = singular. Observing plural sub-bodies within the singular total body. 
For I say that the in-breaths and out-breaths are an aspect of the [larger] body.
Kāyesu [plural] kāyaññatarāhaṁ, bhikkhave, evaṁ vadāmi yadidaṁ—assāsapassāsā.
MN 118
I think body here is the entirety of the six senses. So it is saying to turn the entirety of the six sense onto itself. This has the effect of putting the whole into the foreground and everything within into the background.
This includes the implied point of view. The implied point of view creates the illusion of a watcher apart from the watched. When the implied point of view, the watcher/(the self), collapses into the background, it vanishes. Proliferation ceases. Greed and hatred vanish with the illusion of a separate self. Suffering ceases