I cannot speak for other regions of the USA but the 4-Mess engine has not been a hit with commercial users in our neck of the woods. Here in just our small town we have three 2nd generation equipment dealers that have sold Stihl for years. All three say they'll sell a ton of saws but try to steer commercial users away from the 4-Mess engines.
I suspect Stihl would not be spending the time and money to bring the FS94 2-stroke to the market if the 4-Mess was an overwhelming success. Ditto for Shindiawa's version of 4-Mess. When I purchased my Stihl 4-Mess trimmer the dealer tried to nudge me away from them but my previous 2-stroke Stihl ran great for over ten years so I purchased based on that previous experience.
The 4-Mess was Stihl's marketing attempt to please the tree-huggers. They knew they could meet all EPA regulations with 2-strokes just like RedMax, Shindiawa, Tanaka, were already doing but they gambled that they would be able to lead in a new engine design that would take the power equipment world by storm. I think the design of the 4-Mess is sound but to make it reliable would require a much higher level of quality components and materials which would have driven the cost way up. Add to that commercial users who were used to just keeping a good gas/oil mix in their 2-strokes and nothing else was needed for the useful life of the machine.
I eagerly await the release of the FS94. I e-mailed Stihl to find out the release date but they have not as of yet responded.