When Lupin X shows up, I can picture him playing both sides and trying to get them to work together as a TRUE sentai.

And he'll slowly get them to reveal their identities to each other. Yellow & Green will be the easiest to be the first ones.

So if Hilltop is going to be Patren X, then who is going to be Lupin X?

Patren and Lupin X are the same person.

Wait what?!

It was announced in the catalogue scans a while back that they are the same person who can switch between Lupin X and Patran X.

OK. Well in that case, who is likely to be Patren X and Lupin X?

On second thought, it could however, lead to a possibility of Lupinrangers and Patrangers join forces and fight against Evil together

Zamigo Delma will most likely be Lupin X/Patren X.

That seems unlikely for now. He seems to be following a similar path that villains such as Juzo from Shinkenger, Basco from Gokaiger, and Enter from Go-Busters walked the way. But to give him the benefit of the doubt what is your theory behind that thought?

His monster form is silver and gold.

ToQ6, Zaram, wasn't orange. And looked at what he became. So don't play the "his monster form's colors match" card. LOL. Could be a red herring.