M$ can't add webdav support to skydrive unless they:
a) shrink the storage to somewhere under 9GB
b) make skydrive a paid service
or they do what ADrive did
make two types of plans, a free one without webdav support and a paid one with webdav support.
Why of this, simple, M$ have established a rule that forbids offering FOR FREE, MORE THAN 9GB of storage, WITH WEBDAV SUPPORT.
Obviuosly M$ doesn't want to break their own rules.