Oh! Re the difference in meaning, 'what comes next' suggests a recipient relationship to whatever it is, for example, 'Which metro station comes next?' whereas 'what goes next' is asking what must be done next, as in which piece of an Ikea furniture unit to attach next.

I think single quotes, e.g. 'what comes next,' are better here, at least in American English. I'm too lazy to look up the rules but double quotes mark out unique utterances, whereas single quotes mark out common terms/phrases, for example, a bit of jargon or a slogan.