Nothing is said about what frequency you are using. I wouldn't try this on a 72mhz fm system.
It will probably work OK on a 2.4 system but I wonder if its worth the 2 oz it saves.
An ignition system pulls a heavy current for a short period of time while it charges. The average current it pulls that you read on a voltmeter is no indication of what it takes to charge. It may be several amps for a short period of time. This puts a heavy strain on the regulator. It may not be able to supply what the ignition system really needs resulting in a weak spark at high RPM.
Its simply not a good idea.