We've had capacitive discharge ignition systems available for YEARS in the aftermarket, primarily used in high compression/forced induction/nitrous applications on drag cars. I run an MSD 6A box on my Town Car, which is a CD-type ignition. Moving the capacitor from a computerized box to INSIDE the spark plug doesn't really sound like the brightest of ideas.
You can have all the AVAILABLE power in your ignition system you want; The stock OE Ford TFI ignition was somewhere in the neighbourhood of 38,000 volts and I don't remember the current delivery figure, but is enough to fire even a relatively high compression street engine with ease. This is still overkill by a substantial margin for most traditional I/C engines.
You need enough available voltage and current to bridge the gap on the plug during the point of high pressure (dependent upon camshaft timing, my 302 is ~190psi cranking with ~9.5:1 compression) and this is normally eclipsed two-fold by the available power in the factory ignition system, which is over-powered in case of instances such as an instantaneous lean condition, which will require more power to bridge that gap in a state of compression.
A CD ignition system simply provides more AVAILABLE power at the plug, but the MSD boxes (and others) do an additional thing: they fire the plug more than once. This allows for the ignition of any residual gasses as well; like an advanced version of the dual ignition setups used in the 30's, 40's and 50's on engines like the Van Blerk I4, which had an extremely large bore size, and hence had dual plugs per cylinder to aid in the propagation of the flame-front and ensure more complete combustion. A more advanced implementation appeared on the Ford/Mazda 2.3L I4 in the Ranger and Mustang, the I-4 with eight plugs.
There is simply no logical reason for using these plugs; they will not bridge the gap and spark any "better" than a traditional plug powered by a healthy stock ignition system and I can see them being potentially FAR more problematic, as you are placing the tip of a capacitor into the volatile environment of a combustion chamber, all of which, and even more so in forced induction applications, sees incredible heat.
