You probably know this, but ancient Greek does not use auxiliary verbs to the extent that English does, as it uses inflection to encode tense, mode, and aspect information. The prosdokōmen could be interpreted as present indicative (“are we expecting?”), yes, but it could also be subjunctive deliberative, of which Smyth sez:
> 1805. Deliberative Subjunctive.—The deliberative subjunctive (present or aorist) is used in questions when the speaker asks what he is to do or say (negative μή).
> …
> N.—The subjunctive question does not refer to a future fact, but to what is, under the present circumstances, advantageous or proper to do or say.
So “should we expect?” or “are we (supposed) to expect?” are valid interpretations of προσδοκῶμεν.
> "Take these words of mine…"
As a sibling comment mentions, this is interpreted (eg, Zerwick and Grosvenor on gLuke) as an idiom, but from Aramaic (I don’t know enough about Semitic languages to say) akin to “before your very eyes” in English.
The question isn't one of meaning, but of "register": How polite / academic / lofty / frank / rude / direct / challenging / submissive is it?
In English, "Are you the one, or are we expecting someone else?" the second could also be considered a "subjunctive question" which "does not refer to a future fact", but "what is... advantageous or proper to do or say". All I can say is that, in both cases (in English and in Greek), the question seems more challenging to me than "should we expect another". And I think that interpretation makes more sense of the passage. It's not John experiencing doubt about whether Jesus is the Messiah, nor politely inquiring what his status is: It's John saying, "Hey, I'm in jail; I've passed the torch over to you, but you don't seem to be doing anything. Get on with it!" And Jesus says in response, effectively, "I am getting on with it."
And of course "put these words into your ears" is an idiom -- people don't just walk around saying random things like that. The question is, what's the register of the idiom? "Like Hell I will" is an idiom, which has the same basic meaning as "I will certainly not"; but that doesn't make the latter a good translation for the former. "Let my words ring in your ears" is also an idiom, which basically means "Listen carefully to what I'm about to tell you", but it's a very different register.
Given the contrast between the context ("While everyone was marveling at all that Jesus did..."), and the message (about his betrayal and death) and the fact that even with the colorful admonition, they didn't understand it, I think "Let these words ring in your ears" would be a closer translation than "Listen carefully to what I am about to tell you".
EDIT: Went back and looked it up (Luke 9:44):
Θέσθε ὑμεῖς εἰς τὰ ὦτα ὑμῶν τοὺς λόγους τούτους
Literally, "Put-you into the ears of you these-here words." Θέσθε (put) already is inflected as second-person plural, so ὑμεῖς (you-all) is grammatically unnecessary; the fact that it's included here means there's special emphasis. He says "τοὺς λόγους τούτους" ("these-here words") rather than, say, "τὰ ῥήματά μου" ("my words"). The whole thing just comes off to me as much more emphatic than "Listen carefully".
> 1805. Deliberative Subjunctive.—The deliberative subjunctive (present or aorist) is used in questions when the speaker asks what he is to do or say (negative μή).
> …
> N.—The subjunctive question does not refer to a future fact, but to what is, under the present circumstances, advantageous or proper to do or say.
So “should we expect?” or “are we (supposed) to expect?” are valid interpretations of προσδοκῶμεν.
> "Take these words of mine…"
As a sibling comment mentions, this is interpreted (eg, Zerwick and Grosvenor on gLuke) as an idiom, but from Aramaic (I don’t know enough about Semitic languages to say) akin to “before your very eyes” in English.