As The Command Zone hosts explain in their preview livestream, the word change was required because, without that 'only', modal spells that hit your opponents, but also target things on your side of the battlefield could still be copied
Ungraded & graded values for all MTG 4ED Magic Cards
Even though the ideal switching method is Keldeo-EX plus Float Stone, sometimes your Float Stone get discarded or you can't attach one due to Item-lock (which isn't too uncommon in Expanded with Seismitoad-EX and Trevenant being popular decks), so Darkrai-EX gives you a much easier time switching between Pokemon
That's not good at all, but maybe Nadier's ability will make it worth that high cost
In March of the Machine , Im sure well see many legendary creatures teaming to fight Elesh Norns army of Phyrexians, and the comic book showcase style would be absolutely fitting for a battle of such epic proportions