The thing is, no body wants to make a Swarm Host unburrow because it can't defend itself. This was the same for the lurker back in the day, but the lurker always still had its attack, while the Swarm Host can only spawn units as its offense. I have a simple suggestion:
Give the Swarm Host itself an above ground attack.
It doesn't have to do devastating damage or anything, but it would it not only make Swarm Hosts seem less defenseless when unburrowed (and thus encourage people to actually use it as a mobile unit, like blizzard wants) but it would alleviate some of the problem with needing overt amounts of Swarm Hosts to do significant damage. Why? Well, because Swarmhosts could burrow, spawn their locusts, unburrow, and actually attack along with the locusts. This creates a lot of interesting possibilities for micro and strategy, delaying between movement and counter attacks with the swarmhost itself to try to buy time for the spawn timer, and lets the swarmhost have better synergy with other Zerg units.