They explain nothing. They’re in the same boat as all others: open source will let them keep MV2 longer than mainstream chrome, but that future is uncertain as the main project codebase starts to evolve around MV3 and backward compatibility to hack MV2 back in gets lost over time. Nobody here can make promises, and sites that make that make those judgments are naive.
The Washington district that includes Vancouver has one of the most contested House races in the country this year.