Does this make R’ Slifkin an Apikores? I would say probably not (he does have a fair few Rishonim to rely upon), though it’s clear that several tremendous Talmidei Chachamim think it does.
In all fairness, what I heard (which goes well with the Charaidi mindset) is that the Shittos themselves are NOT Apikorsus. However, bringing these shittos out in the open could cause questions that might make OTHERS become apikorsim or go off the derech.
That makes the question not one of Halacah, but of Hanhaga. Even the Pope is not considered infallible in matters of Hanhaga, only doctrine.