Tom A. I stand corrected...spark DOES have it's place, on giant scale gas burners, but the other 95% of engines, from .01 on up, will continue to use glow...
I'm sure that air start will continue to have a FEW applications, sort of...the new MW44 uses air( I think) or a little electric starter that does not actually fly with the airplane.
But the other 99% of people are going to go air electric start.
As long as you are already set up for air, you might as well keep flying it, they do work, and it's better than no engine at all, but seriously...if you are shopping for a new engine(like I am), unless you are really, really on a budget(some are), would you even consider air start? Especaially when it costs the same or more than the electric competition(mamba?)