Yes, Eventide will be legal for the ICBM Legacy Open this Sunday.  It will be 25-proxy, so if you don't have the Eventide cards yet, just proxy them.  I have heard from some world-class Legacy players that they intend to be there.  Here's who you may have the privilege of losing to:

Owen Turtenwald—GP Columbus 2nd place with Goblins
I@n DeGraff—GP Columbus day 2 with top 64 Slivers
James King—Legacy Worlds 2007 top 8 with Threshold

See ya'll there!