I don't see why they wouldn't be good right away IF they can draft/sign a RT in FA.I don't see why Philly won't have success with him. It'll take a few years, because I don't think they have any of the personnel though.
The teams that added read-option concepts were able to install them over the course of an offseason (Burgundy & Gold, Panthers) or on the fly during the season like (Seattle, 49ers, Miami (to a very limited extent). Likewise the Patriots installed their up-tempo offense during the offseason. These teams had to reach out to or study other teams, sometimes college teams like Nevada and Oregon to install their concepts.
Unlike those teams Kelly won't have to research very much nor reach out to or study other teams because (for lack of a better term) he is the subject matter expert.
Kelly's obstacle is going to be getting the team to 'buy in' and deciding how much of spread option to run. Will they be all spread option all the time? Will they be a WCO that sprinkles in spread option?
I think hiring Pat Shurmur was smart for 2 reasons. And its not because Shurmur is innovative or anything like that. I think signing Shurmur was smart because:
(a) he knows the Eagles and their WCO from having been a coach under and Reid. He should be able to 'translate' the Eagles offense into Kelly's verbiage and vice versa.
(b) he knows how to install/put together an run offense from both the OC and the HC perspective