A silly question.

[Marlowe]

How legal would it be to
1, Play a Wildshape Ranger
2, Swap out your Wildshape for the Aspects of Nature ACF in the SRD?

Since Wildshape Rangers don't get full Druidic Wildshape (they are restricted to small and medium creatures) it is a little dodgy, since you're swapping a depowered version of a class feature for a ACF designed around the full-power version.

On the other hand, Aspects of Nature seems rather underpowered in the first place, but it might appeal to some of us aesthetically. And it gives us a flying archer with angels wings at level 5.

[Acanous]

I don't see a problem with it. Mechanically I'm pretty sure you can pull swap chains so long as the thing you swap out has the correct name.

[nedz]

Since Aspects of Nature is generally used to nerf Druid Wildshaping, then this should be fairly balanced.

[Khedrac]

RAW it's not legal:

Instead of taking animal form, a druid with this variant form of wild shape takes on one or more aspects of nature when she uses her wild shape ability.
However if your DM is open to using the variant rules they should be flexible enough to consider this and judge it on its merits rather than flatly say no.

Edit: it occurs to me that if one is to be very very strict on the grammar then a wildshape ranger could take the ability (it does not say one has to be a druid to take it) but they would be unable to use any of the abilities (as they are not a druid)...