Yesterday a blogpost announced a new feature
for editing Wikipedia from mobile.
http://blog.wikimedia.org/2013/07/25/edit-wikipedia-on-the-go/

Via twitter they confirmed that also Wikisource and all other project can be edited:
do you confirm that? how is the user experience?
Maybe we could file some bugs (if any), to improve the Wikisource editing...
I don't have a smartphone, so I don't know if it is useful for us or not (what about the proofread extension?)

We can contact them at @WikimediaMobile on Twitter.

Aubrey