I am not sure an inflatible seal is necessary if the seal (like our car door seals) keeps out water. The consequences of water entering the coach can be measured in hundreds of thousands of interior work if moisture creates mold and mildew.
Parliament Coach is repairing a Marathon that had slide seal leaks and the entire interior had to be gutted.
With an inflatible seal the slide retraction and extension is a complex series of events including seal deflation, seal vacuum, pin retraction, slide room motion, pin extension, seal inflation, etc. To do that cycle there are numerous valves and controls as well as a control system that senses completion of the various portions of the cycle.
With a non-inflatible seal it is a much simpler control system and in fact we three looked at a plastic coach with non-inflatible seals and the set up looked very good. We aren't the engineers so these thoughts are nothing more than me shooting from the lip.