I think Sagitar will be a really cool inclusion into the Classics line. I'm not exactly sure how he'll be engineered but I think we'll need to see Stridor and Nightstalker before we get a better idea how his mechanics will work. (i.e. are their hind quarters manueverable enough to stand on) If he has any reused parts, it would likely be from the techno-horses, imo.
He will probably be impressively large when standing. In my mind taller than Shadowbeast but smaller than Megator.
So bring him on as a quarterly, if I ventured a guiess I'd say between 2014-2016.