It looks like a good idea. I haven't really looked in the source code but I'm wondering how the bot does certain things:
* A pull request can contain of multiple commits. Do you on every commit to the pull request squash them into one and push that up? (this might be gerrit specific; I actually don't know how it'll work on Phabricator) * What about comments? I think comments should appear on the respective other site (e.g. Legoktm commented in gerrit: that should show up in github (you might be able to associcate the users using the e-mail addresses)). Afaik it's possible to add comments to certain lines in github like in gerrit but as you need to squash that into one commit I don't think there is a sensible mapping. * Similar to comments: Maybe Jenkins' result should appear in the pull request. * And a small feature request would be that when the bot comments that it has been synced with gerrit, you should add the gerrit id.
And the comments are an important feature. Without showing the comments on the respective other site I don't think this is worthwhile as the author basically gets no feedback on their code.
Fabian