Firstly, IANAL, but I have legal textbooks, and it looks like a very poor case.
Katie Hopkins and Jack Monroe was totally different. KH misidentified a picture of someone being a prat on a war memorial as Jack and tweeted that out.
That is nothing like someone being sarky about the implications of your tweet. Any reasonable person on the clapham omnibus could tell quite clearly from the quote tweet of Omid's tweet at the top of Dr EM's thread, what was going on.
Secondly, a legal case would be a PR nightmare for Djalili. No-one outside twitter and MN knows about this at the moment. That is not something he should work to change.