Well X disbanded and so S.K.I.N is his last band really.Of course X will do that reunion(so we hear) but theirs no way they can get back together Toshi said he wouldn't sing the violent songs like Kurenai etc and if Yoshiki was to write more they would be violent and Toshi wouldn't sing.
Well, to be honest I don't think they're even gonna reunite at all. First, because I see both Yoshiki and Toshi both very dismotivated and unsure about it. (and I can't imagine Heath, Pata or even Taiji all excited about it). And second because it would make no sense to reunite a band for a mere tour or live when that very same band has even done an official
Last Live. And moreover, as you said, Toshi won't sing most of the songs. (so X will reunite just to sing Forever Love, drop some Tears and go back home under Endless Rain? nope. don't think so).
But of course, this is just a personal oppinion, I hope I'm wrong. But yes, under that point of view, SKIN is probably his last band. What I mean with X being his
first and last band ever is just a metaphor for X being very special for him, forever.