I think if the introduction of a send-off was introduced on the basis that it is intended only for use in those rare instances of clear cut violent acts, eg Gaff, Bugg, Jonas, Hall, then I think that's fine.
Anything more than that and it starts getting tricky. I'd hate to see a situation where a send-off is applied and that player is subsequently cleared at the tribunal.
Limit it to account for the severe and rare egregious cases that are beyond any doubt, then I'm okay with that.