In my opinion, adding the s+VS1 variation sequence is completely unneeded. If you really want a "long s", use the code assigned to the long s. fonts or renderers should still provide a reasonnable fallback to "s" if the glyph is missing.
This means that all existing ligatures will long s will continue to be encoded as well with "long s" and ZWJ. the "x+VS1" proposal is an attempt to disunify the "long s", when it is NOT needed at all. The only convenient variation sequence would be to add "S+VS1" for the capital (because long s has no capital) only to preserve the long s semantic when converting it to uppercase or titlecase, in which case the mapping of "S+VS1" to lowercase will give again the standard "long s".
