Neven been a Zep fan - I can't relate with Plant's singing or his lyrics, even though he is in a league of his own -, but Zep touring without Plant as Zep is like Paul McCartney and Ringo hiring two guys and calling themselves The Beatles. Or the Rolling Stones continuing without Mick.
Plant was/is more than the singer of Zep, his voice (more than with other singers because he was never one to transport any relevant lyrical content!) is a key part of Zep's instrumentation and overall sound.
We already have to suffer with "Queen + Paul Rodgers". I have no appetite for "Led Zeppelin + Chris Robinson" or whoever they plan to get. I'm fine with Page and Jones getting back together and recording a new album under a new moniker though.
Uwe