It would be relatively simple to do. This is the structure that current armies are built around:
Attachment:
Old Structure.JPG [ 18.86 KiB | Viewed 4057 times ]
We could just implement something like this:
Attachment:
New Structure.JPG [ 36.49 KiB | Viewed 4057 times ]
Company, Special and Support stays the same, but each formation can take transport options and/or upgrades (another area that we could still explore?).
Obviously some units could fit under Support or Transport options like Land Raiders and their variants as you might want some in your army for their firepower rather than their transport capability. I guess we add the caveat that formations chosen as transport options, are considered part the formation they are transporting and must maintain coherency, but if you choose to take them as a Support option, but use them as transports, then they are considered separate units.
Also need to figure out what to do with HQ units. Do we allow just them to take a free vehicle that matches the transports of one of the detachments in the company?
The only significant issue I can see is their might be a slight increase in VPs since each formation/option will have its own VP/BP value and they then get added together.
For example, take a generic detachment of infantry and their vehicles, 6 stands, 3 vehicles. They cost 300pts, give 3 VPs. If separately the infantry costs 150pts (2 VPs) and the vehicles 150pts (+2 VPs), the VPs of the combined unit is now 4. Given that this will be applied across most, if not all army lists, I am not unduly worried as every one will be in the same boat.
Or rather than just adding the separate VPs/BPs of the units together we state that people have to work out the new combined VPs and BPs from the total cost of the combined formation and total number of models.
A word of warning, if I do go down this route with the marines, I will be restructuring all the formations so they are based around 6 stands of infantry and 3/6 vehicles (though this will only affect Legion of the Damned, Terminators and Grey Knights from what I can see).
Matt