It would be great if you expanded your question

Question

Imagine there's a very short question at this site, and I'm uncertain what the poster intends to ask.

Should I write

1. It would've been great if you'd expanded your question. (matrix clause: Past Perfective modal, conditional clause: Past Perfective)

Or

2. It would be great if you expanded your question. (matrix clause: Past modal, conditional clause: Past)

Or

3. It will be great if you expand your question. (matrix clause: Future modal, conditional clause: Present Simple referring to the future)

I'm not sure about sentence 1. The verb "expanded" calls for a future action, but in sentence 1 we describe an unfullfilled condition in the past.

Or maybe the construction of sentence 2 is used to refer to a situation that is already "over" and it too far in the past to serve as a hint that I want more infornation now. Maybe such construction would be more suitable in "I remember that question you posed 2 years ago. It would've been great.."

Sentence 2 is what is called a "second conditional", and it is said that a second conditional describes an improbable sutuation in the present. Would it be suitable?

Or does the verb expanded makes the first two options awkward semantically?

Sentence 3 describes an open (possible) condition, but isn't it a bit too mandative?

Answer 1

It would've been great if you'd expanded your question.

This implies that the there is no longer a possibility of the question being expanded by whoever "you" is, i.e. it was deleted or locked, or the speaker/writer believes the asker is not returning.

It would be great if you expanded your question.

This sounds good, and this construct is frequently used (esp. in a business setting in my opinion) to politely ask someone to do something.

It will be great if you expand your question.

This means the same as the sentence above. I agree that it can come off as too "mandative", as you put it, if the listener/reader isn't aware of your tone, so I suggest the second sentence.

Can #2 be taken to mean "It would be great if you expaned your question (in the near future)", or would it always mean an unreal/improbable situation in the present,

"It would be great if you X" will usually be interpreted as a request. "It would be great if {third-party} X" can be interpreted as a indirect request if the listener has the power to influence the third party.

Something like It would be great if a new road were built here has a conditional meaning - there is not actually a new road, it's a condition to "it would be great." It's not always used to refer to improbable events (is it really impossible that there will never be a road?), though it can - I would freak out if I ever were to see a unicorn in real life.

Answer 2

It would be great if you expanded your question.

Paraphrase: I wish you would expand your question. The tense-shift (expanded) is perfectly idiomatic to my AmE ear.

It would've been great if you'd expanded your question.

Paraphrase: Too bad you didn't expand your question when you had the chance. Modal and tense-shifts again are perfectly idiomatic to my AmE ear.

It will be great if you expand your question.

This strikes my ear as ungrammatical. "Will" and "if" together like that are grammatically dissonant. The sentence becomes idiomatic when "if" is replaced with "when". It will be great when you expand your question.
Paraphrase (with "when"): The question will be a great one when you expand it.

Answer 3

The four conditionals often taught in textbooks are common patterns of often more complex underlying grammar of expressing conditionality, the hypothetical and unreal, requests, wishes, etc. So we should not be surprised when we encounter or want to produce text that doesn't neatly align with a particular grammar.

The if clause in the second conditional is often improbable, or relatively improbable, but not always: If you left now, you would easily get home in time.

We can say this without necessarily conveying improbability.

Also, it may be that we sometimes use the improbable implication as a sort of proxy to actually communicate politeness by softening. Our statements in this form are often more clearly interpreted as more suggestion instead of expectation. This is tricky territory, because would and could as modals can convey either or both politeness and request senses.

Some additional options:

It would be great if you could expand your question.

Could you add some more information to your question so that it's more clear or precise?