Not yet!
Webmentions look like something the team has in mind for incorporating into future Write.as’ commenting system, Remark.as. The feature is brought up here.
Will keep looking into webmentions though. In the meantime I have been thinking about how to incorporate light webmention-like functionality with my Write.as blog, like notifying me when someone mentions my blog on Read Write.as.
Would even that be of interest?