The thing is “one-state solution” means three different incompatible things: displacement of Israeli Jews, displacement or political suppression of Palestinian Arabs, and a multiethnic, multireligious democracy. You can’t really add up support for all three and call it support for one thing.
two state solution won't be taken off the table, it's just a scare tactic. but even if it were, chance that support for it will skyrocket in Israel is non-existent.
I don’t think it is fair to generalize over such a vast region by making grand statements like “they truly believe...”. In fact most Kurdish autonomous regions were pretty quick to adopt democracy as their system of choise after they liberated them self from the Islamic State terrorist group during the Syrian civil war. And popular pro-democracy uprisings in Yemen would suggest counter to your statement.
This is different from annexation which would basically mean a surrender for the Palestinians. Israel would continue as is with the current constitution. Palestinians would become Israeli citizens but on the terms of the Israelis.
https://en.wikipedia.org/wiki/One-state_solution