Bismarck,
You are quite correct that Amphibeous Ops are here to stay - they offer an effective way for govts to influence, deter, fix or, ultimately, engage with hostile forces. To be effective you need the correct shipping and trained staff officers; you don't need CHF....though it is doubtless more efficient with them. The LitM RW capability will not expand; TAGs will always seek to draw in components that offer complimentary capabilities (esp CH47 and AH) so any "uplift" will be from existing JHC fleets. I'm sure a large chunk of the post-Afghan "regeneration" will be spent trying to get the CH47 and Puma 2 fleets back up to speed for LitM (not to mention a large % of CHF who've never embarked due to the Herrick focus...).
MM4; I don't see any issue with a 4* soldier or sailor being the SDH for air assets under their command. One could argue that what does a FJ CAS know about the issues of RW or AT fleets? The answer is a robust chain of ODH/DDH/SO to provide that expertise, as happens now.