It is important to understand the fundamental purpose of Romans 9. It is part of a bigger chunk, chapters 9 to 11, which is fundamentally Paul's treatment of how Jew and Gentile have been brought together in the purposes of God. And in Romans 9 Paul is talking about Israel and her plight.
The question of any general theology of individual pre-destination with no reference to Israel in particular is simply not the problem that Paul has put on the table. The problem is Israel and her sad condition:
I speak the truth in Christ—I am not lying, my conscience confirms it in the Holy Spirit— I have great sorrow and unceasing anguish in my heart. For I could wish that I myself were cursed and cut off from Christ for the sake of my brothers, those of my own race, the people of Israel.
And at the end of the chapter, it is clear that Paul is also focused on Israel and what has happened to her:
What then shall we say? That the Gentiles, who did not pursue righteousness, have obtained it, a righteousness that is by faith; but Israel, who pursued a law of righteousness, has not attained it. Why not? Because they pursued it not by faith but as if it were by works. They stumbled over the "stumbling stone." As it is written:
"See, I lay in Zion a stone that causes men to stumble
and a rock that makes them fall,
At the beginning of the chapter has Paul given us any reason to expect that he will shortly be giving a general theology of pre-destination. No. It is Israel that is the issue at the beginning.
At the end of the chapter, it is clear that Paul is talking about what God has done to Zion, yes Zion.
And a concluding statement that God has taken action to make Israel stumble, following an opening statement about the sad state of Israel gives us every reason to think that the vessels of destruction are, yes, Jews.
It is the Israel question that is on the table.
Paul concludes with a clear statement that God has done something to Israel that has mad her stumble and not attain righteousness.
He is, of course, giving us every reason to see the vessels of destruction as being hardened Jews (even if they are, of course, each "individuals").
And he has given us no reason to think that he is interrupting the clear flow of an Israel argument to make some kind of general statement about individuals are pre-destined, regardless of their ethnic status.
This is a treatment of Israel, not humanity in general. And this is so even if what has happened to Israel has indeed benefited "vessels of mercy" who are both Jew and Gentile.