Complex? Heavy?? Unreliable?? Surely you jest....You would need a generator not unlike those found on saws with heated grips, some sort of ECM, a single DI injector, a fuel pump and an oil injection system. People add as much weight or more adding longer bars and wrap handles.
As far as reliability, Ski-Doo ETEC powered sleds and Evinrude ETEC outboards have a pretty solid track record from what I can see. Still in production and selling well after all this time...
As to your question of how it could ever be made small enough for implementation on hand held power equipment... Have you been asleep for the last 80 years of industrial and technological advancement??
I'm not trying to be a dick, but naysaying isn't a valid argument when there are very successful systems in the market that have held up, granted in larger scale.
It's only a matter of time man, you will see it..unless of course battery power ends up taking over completely, which is a very real possibility. We should probably start figuring out how to port battery powered saws now and get ahead of the competition