Hmm, hard to say.
I’d think some idioms can’t be traced back to underlying forms which can be used idiomatically as well.

cé uaidh a dteastíonn …

Beside this all are (grammatically) right.
I’d prefer those with cé leis …, cé uaidh …, i.e. leis and uaidh next to cé.

WOW!

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Hmm, I've thought recently about such questions and I've found this thread again.

I really wonder how to translate such questions as "Who would like ..." or "Who prefers ...", i.e. how to use such modal expressions in questions.
I had recommemded Cé leis ar mhaith etc. but I doubt this now.

I'd rather say:
Cér mhaith leis caife? = Who would like coffee?
and
Cér fearr leis tae? = Who prefers tea?
or
Cérbh fhearr leis é sin a dhéanamh? = Who would prefer to do this?

But ...
I could not find many examples in corpus.focloir.ie or in Google, almost no examples at all - neither for Cér mhaith leis nor for Cé leis ar mhaith
Why?

Does no one ask such questions in Irish?
Or do they use a different form?
Questions like Cad is fearr leat? Cé acu ba mhaith leat? are very common but not those above ...

hahaha rinne tú é chun náire a chur orm. Nach dochreidte an rud é cé chomh holc is a bhí mo chuid Gaeilge ag an am sin? Tá súil agam go mbeidh mé in ann an rud céanna a rá i gceann dhá bhliain faoin gcuid atá agam anois!

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The tendency (not sure if it is a rule) for prepositions to follow directly after the question word seems to me to be powerful. I would probably prefer Cé leis ar mhaith in this context if I thought of it, although I would be more likely to spontaneously create the other. Of course, with practice I could easily change that likelihood so it isn't very meaningful.

Consider also this interesting selection
Cér mhaith leis a phósadh?
Cér mhaith leis pósadh?
Cé leis ar mhaith pósadh?

Two with one meaning, one with another, two with one structure, one with another, but the groupings are different. Be eliminating the one, we have a more pleasing dichotomy. But shall we?

I have encountered before this sentence (I think I am remembering it verbatim):
Cad air ar mhaith le do mhac staidéar a dhéanamh?
It was from a source I consider reputable. This also leads me to lean towards your initially suggested word order. Leaving aside the contraction cér, there are probably more examples with cad or céard to be found.

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A phrase like is maith liom is a unit. This unit is the predicative of the sentence. So, it should be (part of) the predicative of a wh-queston, as well.
But if we tear it apart by saying Cé leis ar maith [caife]? this unit wouldn't exist anymore. The relative clause ... ar maith [caife] would be subject, cé leis being the predicate. I'd guess this is the reason why it sounds strange and perhaps is wrong.
In Cér maith leis caife? the unit is safe: cé + ar maith leis + caife.

But still, apparently nobody (?) says so.
I found only one (!) example in this nice grammar page about copula constructions ("Long Kesh Documents", https://sites.google.com/site/longkeshd ... an-chopail) I haven't seen before.
The unknown (?) author recommends Cér maith leis ...?.
But there are a few other minor errors in this page so I doubt I can rely on such a single mention.
Usually grammar books say that these indirect relative copula constructions with "cér" (cé + ar) are rare. They mention Cér díobh thú?.



The first is Who'd like to marry him?, the second (and third) Who'd like to marry?



Here, the unit ba mhaith leis is unchanged.
Staidéar a dhéanamh air isn't such an inseparable unit, so separating air is okay.
The same is true for most prepositional phrases, so you can ask cad air, cad leis, cé faoi, etc.

What I am gleaning from Learning Irish is:

Cé a mba mhaith leis ...

So:

Cé a mba mhaith leis caifé a ól?
Who would like to drink coffee?

ar can be substituted for a mba, giving:

Cé ar mhaith leis ... => Cér mhaith leis ...

But you said there is no sign of that in the Corpus, a Labhráis.

How about Cé agaibh ar mhaith leis ...?


Bríd, how would _you_ say "Who would like tea? and who would like coffee?"

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WARNING: Intermediate speaker - await further opinions, corrections and adjustments before acting on my advice.
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

Good idea to write it big so I'd see it.

Personally I'd say:
Cé 'tá 'g iarraidh tae, nó 'g iarraidh coffee?
including "agaibh" is optional in speech, but can be added to stress it.

GRMA, a Bhríd.

Maybe Labhrás is right. There are some constructions that Irish speaker just naturally avoid.

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WARNING: Intermediate speaker - await further opinions, corrections and adjustments before acting on my advice.
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), agus Gaeilge an Chaighdeáin Oifigiúil (CO).