If an opposite-sex couple kiss, both are JWs, truly single, and it was consensual, even if they weren't officially dating, I don't believe any action would take place, although they would probably be warned that kissing might lead to more. However, if one was a JW and the other a non-JW, although it's not likely the JW would get disfellowshipped (although I suppose anything is possible), the JW would likely be reprimanded. No dating (including no kissing) outside of the faith and only in a serious dating relationship leading to marriage.
With the same-sex couple who only kiss, are both JWs, truly single, and it was consensual, and the elder body heard about it, there's no doubt that there would be a witch hunt with an attempt to bring them before a judicial committee. I think they might at minimum be privately reproved, but if one or both appeared to be unrepentant - even over only a kiss - certainly the elders could find a way to disfellowship one or both of them.
Perhaps those who have more recently been elders can give their perspective.