EP was a better clutch design than the Intense LSD, from what I heard, but still not a great solution. Never heard of Phantom.
The engines are plentiful, but the small modding market is one where most buyers are on a tighter budget than what can support robust mods for 400+whp builds. You see plenty of near-stock bolt-on guys, and 300-350whp setups still buying up things sporadically, that they don't actually need... That, however, didn't support the manufacturing of more trans upgrades or engine items beyond they heyday of the 3800's. People get frustrated if there's not a simpler path to "parking lot pimpin" their car, because regardless of performance, if the car doesn't also draw looks and sound great, it doesn't meet the need of majority of the "car crowd." (Enter the 14-15sec Mustang GT market doninance of the past 40yrs, riding the coat-tails of the few who put in the time/money to make some absolute monsters that built a brand name.)