From High Elf point of view, the difference is academic at best. Last time, they intervened because Dieter (or was it his successor) was being a shitter and trying to conquer a province Dieter's own stupidity turned independent. Since he was acting like a crazy asshole, I would not put it past High Elves to have expected conflict with him, and simply used Marienburg as the battlefield of choice. In that case, the province remaining independent benefits them, as it provides a buffer zone and meatshields.
In this case, the emperor seems reasonable, and appears to have the support of both the Colleges and the Dwarves (which, or course, Dieter did not have, for obvious reasons). Marienburg would be initiating the hostilities and weakening a major bulwark against Chaos, Orcs, Skaven and Beastmen out of nothing but jealously, fear and greed. Basically, in this case, Marienburg would be the Dieter. And elves won't die for that shit. Especially since the conflict would not be anywhere near as one-sided as it was last time, when the empire lacked the Magical and Anti-Magical forces required to counter the elves.