Is "did" used conditionally, regionally or otherwise? e.g. "Did you want..." instead of "Would you want..."

This use of the past is called "attitudinal past" in A Comprehensive Grammar of the English Language (Quirk et al.); the present can be used but the past introduces an element of politeness.

(CoGEL § 4.16) Meanings of the past tense with reference to present and future time

Just as the simple present does not always refer to present time, so the past tense is not always confined to past time reference. There are again three special meanings to mention:

(a) In INDIRECT SPEECH (or INDIRECT THOUGHT) […]
(b) The ATTITUDINAL PAST, used with verbs expressing volition or mental state, reflects the tentative attitude of the speaker, rather than past time. In the following pairs, both the present and past tenses refer to a present state of mind, but the latter is somewhat more polite:
• Do/Did you want to see me now?
• I wonder/wondered if you could help us.
(c) The HYPOTHETICAL PAST […]

A matter of context (addition)

I am at a complete loss as far as providing the least information on regional practices concerning this usage, but I think there is a matter of context relative to it that is not mentioned in CoGEL, and the principle that became apparent to me in connection with this matter never seemed to be contradicted in all the dialogue I could hear and read. Let's narrow it down to examples.

Example

Person A is conversing on the telephone with person B and has told B that he is planning on meeting him sometime in the future; the conversation, as it goes on, is being diverted on various subjects, without anything having been settled about the meeting. Then B has a choice of tense between present and past if he wishes to ask about the date when the meeting would be convenient. (The present is the so-called "state present", which is used for actions or conditions that were true for an indefinite period of time in the past, that remain true now and that will remain true for an indefinite time period in the future. It is hence understood that the possibility of using the past makes sense.) For instance, he can say "When do you want us to meet?" or "When did you want us to meet?". It is even possible that a date has been arranged in the conversation that precedes but forgotten by B, or at worst, the mere insinuation of a possible meeting has been made (by A, important), and those cases allow still for the same choice. The gist of the matter is that there must be a background in the context in which the question finds a justification. Otherwise only the present is correct ; if B wishes to use a more polite form, B must use something else than the past (would). But that is not all; if the idea of a meeting is B's, and even if the idea was formulated by B at the beginning of the conversation, B has to use the present, which is now the "instantaneous present" (action or state begun and terminated approximately at the time of speech).

Other example

(CoGEL § 14.34 Note) [b] Backshift normally occurs in the subordinate clause after an attitudinal past used for politeness:
• What did you say your name was?

In this example also it is clear that the name has been given to the speaker at some time in the verbal exchange. We understand also that if this is not the case, then "is" has to be used instead of "was".