RORY: What’s [Jess] like?
LORELAI: Well, he’s not gonna be subbing for the new dodo on the Regis show any time soon, let’s put it like that.
A reference to the talk show hosted by Regis Philbin, previously discussed. His co-host since 1988 was Kathie Lee Gifford, when it was called Live! With Regis and Kathy Lee. After Gifford’s last show in 2000, Regis spent six months auditioning possible co-hosts live on air. In February 2001, he chose dancer and actress Kelly Ripa, and the show’s name was changed to Live! With Regis and Kelly.
Kelly Ripa seems to be “the new dodo” (the new idiot) Lorelai is referring to. She’d been co-host for nearly seven months at this point, but I guess that’s still new for someone who is used to Kathy Lee Gifford.
“Subbing” is short for “substituting, so Lorelai is saying that Jess isn’t suitable to fill in for a talk show host (i.e., he isn’t chatty).