Well, with enough lore re-adaptation, you could make such a game possible, though you could hardly call it an UFO experience through the lenses of the aliens.
Let us work with the idea that we are a bunch of fleeing Sectoids, Hybrids or any similar lowly race with some end game potential (sectoids are, at least, psychics). You are fleeing from the empire, and decide to establish a base of operations on Earth. However, that will not be 1999 X-Com earth. Maybe it will be in the future (say, Apocalypse future) in which X-Com is hardened and well prepared for an alien invasion. Maybe it is in the future in which X-Com failed and humanity is on its way towards uplifting, as in XCom 2.
Regardless, you will start off weak, taking down supply ships and the such to get money and material in to upgrade your base and hopefully build another one (or not, in case of a single base game sounds more interesting for the proposal), all the while the alien empire mostly ignores you, until you become enough of a problem for them to go and knock on your door.
Basically it would be something between Piratez (guerrilla game) and XCom2 (minus base mobility).