The Greek text of Luke 17.20: ἐπερωτηθεὶς δὲ ὑπὸ τῶν Φαρισαίων πότε ἔρχεται ἡ βασιλεία τοῦ θεοῦ… “Asked by the when the Kingdom of God comes…”
The verb here is ἔρχεται (erchetai), present indicative active, 3rd person singular, of the verb erchomai (to come).
So: it is neither a conditional nor a future. It is a present with the value of a near future, very common in biblical Greek.
One could translate literally: “When does the Kingdom of God come?” or “When is it that the Kingdom of God comes?”
Comparison with “will come” or “would come”
“Will come” is in the simple future: it expresses a certainty that an event will happen in the future. Example: The Kingdom of God will come.
“Would come” is in the present conditional: it expresses a hypothesis, an uncertainty, or an action that depends on a condition. Example: The Kingdom of God would come if…
“Comes” is in the present indicative: it can denote an action in progress or imminent, sometimes used to speak of a near future. Example: The Kingdom of God comes — it is already at work.
In Luke 17.20, “will come” is a good dynamic translation, because it conveys the idea of an expected event. But “would come” would be incorrect here: the Greek expresses neither hypothesis nor uncertainty.
In summary
The Greek text uses a present indicative active (erchetai), not a conditional. It expresses a real and certain expectation, not a mere possibility. Translating by “will come” is faithful to the meaning, but “would come” would weaken the force of the text.