In all of the descriptive dictionary definitions of “emoji” I've encountered thus far (e.g. Merriam-Webster entry), the plural of emoji is given an optional “s.”
plural emoji or emo·jis
In the responses to When was “emoji” first used?, the term is described as a Latinized version of its Japanese progenitor.
Though it doesn't follow the Latin pattern exactly (there is no emojus of which I am aware), does its Latinization lend any credence to an argument in favor of using emoji for both the singular and plural form of the noun (i.e. as a defective/invariant noun)?