They obviously considered the bladder option when designing the craft, which means that: - either air and He separate fast and well enough to make it unnecessar

They obviously considered the bladder option when designing the craft, which means that: - either air and He separate fast and well enough to make it unnecessary; - or there are big problems which make the bladder impractical. I have no idea what these problems might be. Anyway you're right: a scientifically literate journalist would probably have explained the rationales behind this non-obvious choice.