So what happens if i return a Nameless Inversion to the battlefield? My gut says that SBE's will put in the graveyard again but I wonder how this works oficially?
Assuming no rules changes with RIX's releaae: it just can't happen.
304.4. Instants can't enter the battlefield. If an instant would enter the battlefield, it remains in its previous zone instead.
307.4. Sorceries can't enter the battlefield. If a sorcery would enter the battlefield, it remains in its previous zone instead.
Instant and Sorcery cards can't enter the battlefield, under any circumstances. Nameless Inversion is a valid target, but when the ability resolves, the impossible action simply isn't performed. Nameless stays on the graveyard.