Why would using Stillpoints under your speakers make setting them on top of carpet ok? Carpet will allow your speakers to rock back and forth unless you spike through it. That is not a desirable thing. Stillpoints work in the vertical plane which is not a problem for speaker drivers. If you get horizontal movement from the speakers rocking back and forth on the carpet then it will counteract what the speaker drivers are trying to do. This will result in muddled sound.
Regardless of the surface below the component, the performance of any of the Stillpoint Ultra products is all about proper loading of the technology pocket(s). Proper loading is accomplished on carpeted floors. Please consider the following. Don't reason yourself into a belief or position on this issue, but let your ears guide you (where have I heard that before? ). Rather, setup a A/B test in which you listen without the Stillpoints product and then with the product. I believe you will hear the benefit of isolation.
That said, there are still people with concerns. We want to address those concerns so we are in the development stage of testing spikes beginning with the Ultra 5 product. Using spikes should not prevent proper loading. Testing spikes came about as the result of a related project with the Ultra 5 and KEF Blade speakers. The shallow tap on the Blade cabinet (5 threads) presents an issue leveling the speaker when used with the standard Ultra 5 and adapter. We decided to provide additional leveling between the floor and bottom of the U5. We commissioned our machinist vendor to put a 1/2-20 tap in the bottom half of the U5 and then used our 1/2-20 to 1/4-20 adapter to attach a Ultra Base. Tightening the adapter into the U Base allows us to use the deep tap of the U5 bottom to provide the desired leveling adjustment distance. The logical progression was to commission spikes. We have prototypes but they need some redesign and we are working on that. I don't have a timetable for testing but rest assured I will report back to the forum once we have been able to test with spikes.