A solution doesn't have to move us away from fossil fuels all by itself to be a useful piece of the puzzle. Even if heat pumps were only viable in places that don't regularly get super cold in the winter (which isn't true), that's a huge number of places covering a large portion of the population. A lot of the US, for example, gets hot enough in the summer that you want central air conditioning but also gets moderately cold in the winter. A heat pump system can cover you all year round with the same exact system. If you install a backup heat source, which can be electric by the way, that covers even more potential installation locations.