Thank you GrandTourer for that info. I'm looking into the cost. We would expect some minor trimming on the interior pieces. The main issue is whether the bumper cover fits. The rest is doable.
Whether its worth it to someone is highly subjective. On the basis of looks alone, maybe not. But I am more interested in the aero effect, plus even better cooling. Porsche does a real good job designing aero on their cars. Aftermarket splitters are still not readily available for the 981 cars, and those that are, aren't cheap or particularly well made. Often, in order to be strong and stable, they have to be secured to the bumper cover, which means that if the splitter gets ripped off, then severe damage is likely to the bumper cover as well. Now, instead of $500 - $1000 repair bill, you're looking at something considerable more. The splitter on the GT4 is designed in such a way that if some damage occurs, you only have to replace the plastic splitter instead of the entire bumper.
Venting the center radiator up with properly designed ducting, also adds to downforce.
Plus, it just looks right.