I think the landing craft would largely be consigned to the scrapheap if we put it in the air allowance given how much it takes up
I think the marines were always meant to be more flexible so you could create very specialised taskforce-style armies compared to the more homogenous guard regiments
On the flyers, I'm with you there, I'd prefer to see the new flyers adopted across the board for all new marine lists and am trying to encourage that with all currently in-development lists
I'm loathe to make significant changes to the codex list (barring the thunderhawk one) as it's one of the most balanced, flexible lists we have, it makes a very good list to test against (basically if I beat dptdexys using his marines more than my usual 'once in a blue moon' frequency, then that is a good indicator the list I'm using may be a wee tad overpowered)