If we ever get to fusion or other unlimited energy source, it may be possible someday to thoroughly transform Titan, relocate 100,000 people on it and flung it in to space to another star. Titan can be our "generational spaceship" that goes forever to infinity and beyond. To colonize galaxy, using moons as spaceship would be necessary assuming there is no way to travel faster than speed of light. So all inter-galactic spaceships needs to be generational, completely self-sufficient in every possible way and have enough population that can evolve without too much of inbreeding for thousands of years.
That's making a lot of assumptions though. For one thing, I think to become an interstellar species, we'll have to direct the evolution of Homo sapiens into some kind of Homo exteriores spatium sapiens. Radiation-hardened, very very long lived, happy to live together in very tight spaces, etc. Might look closer to giant cockroaches than hairless apes. It certainly seems we're a lot closer to the ability to do this (eg. CRISPR-Cas9) than colonize & move a moon.
