Is the use of "would" valid when describing a hypothetical, future situation?

I'd probably class this as an example of a sentence that you may well get in spontaneous speech, but which if you were sitting down and editing it in writing, you'd probably avoid.

The usual case is for the modal would (or 'd) in the main clause to accompany a past tense in the if clause, and for a different modal to be chosen if the main clause is non-past.

However, would isn't exclusively used with a past tense. People would commonly say in isolation e.g. "You'd do X" to mean "generally, in the universe, under a whole variety of conditions or if any of a range of conditions occurred, one would do X" -- in other words, this utterance is then not necessarily bound to any reference point of any particular time.

Looking at it retrospectively, the sentence as it stands is a little odd because this "tenseless" use of would clashes with the reader's usual expectation of a past tense. But the sequence isn't per se impossible, and you can make your sentence sound more acceptable by masking the clash, e.g.:

"If you feel like that, the general expectation is that you'd say something."

So if you heard your example in speech, I think what you have is effectively a spontaneous sentence based on the thought process of the latter example, but poorly phrased when one has the chance to judge and revise it retrospectively.

This kind of question has been asked on this forum too many times.

Basically, there exist a confusion as to why a past or past perfect could be used to propose or imagine a present or future action. How could you use a past tense for present or future action.

I want to give people puzzled by this practice starting with the ground-zero reason.

Nonfinite

First, you need to understand the nonfinite concept. There are various pronouncements as to what nonfinite actions or clauses actually mean. If you look at it thro the lens of event-state model, nonfinite action is temporally unbounded action. So that nonfinite is not restricted by tenses. You may use a past/present/future to express nonfinite, but the action clause itself is modularly encapsulated so that it can be floated across actual time and deployed without change of its tenses.

The most well-known nonfinite is the infinitive.

• Did he come here to die?
• Will he come here to die?
• Can he come here to die?
• Is he here to die?

Less well-known and quite misunderstood is the to-less infinitive. Misunderstood because people often assign singular-perpetrator to the verb (he dies instead of he die). The infinitive is also independent of the number of perpetrators of a verb.

• I wish that he die before being crowned the king.
• I had wished that he die before being crowned the king.
• I will wish that he die before being crowned the king.

Gerunds are also nonfinite.

Subjunctive action (aka mood) is one particular class of nonfinite that is quite familiar to most speakers of European languages. More accurately, languages that had been influenced by Latin.

Subjunctive

If you are familiar with real and imaginary mathematics, you should classify subjunctive action as imaginary action. A non-mathematical approach would classify subjunctive as a "mood" as it does not represent actualized action. There is the English grammar definition of subjunctive and there is the generic linguistic definition of subjunctive that covers all imaginary (whether proposed, optional, imagined or delusional) actions. English does not have a separate set of tenses for subjunctive and therefore borrows tenses from the real world.

Obviously, imaginary action is nonfinite, i.e. unbounded to real time.

• If I were a bird, I would soar to the skies.
• Were I you, I would marry him immediately already.
• Were I you, I would have married him immediately already.

• If you died tomorrow, your insurance policy would pay your family $3 million.
• Don't worry. If I felt bad, I would tell you.

• Had he died last year, his insurance policy would have paid his family $3 million.

• Could you please take your shoes off?
• I would like to know if I could have another bowl of soup, sir.

I always like using the optative to illustrate subjunctive/imaginary action. Instead of saying
Can you take your shoes off?
modern languages have developed the etiquette of self-condescension to declare that "I have an imaginary delusion that you would take your shoes off" as a politeness.

So that in such societies where optative is often used, asking "Can you take your shoes off?" would sound commandeering, abrupt and even rude.

In conclusion, to answer the question of your specific case, the rule sequence is
nonfinite > subjunctive/imaginary > conditional:

If you feel that way, you would say it.