Should Marvin Lewis be in the Ring of Honor some day?

[*ochocincos*]

That's tough to say, as Marvin was good, not great.
As others have said, I'd put Wyche and Gregg in over Marvin when it comes to coaches.
You also have a lot of players to put in too before Marvin should be considered.

Players and coaches I'd put in ahead of Marvin (not in any order):
Chad Johnson
Reggie Williams
Louis Breeden
James Brooks
David Fulcher
Willie Anderson
Lemar Parrish
Corey Dillon
Tim Krumrie
Isaac Curtis
Cris Collinsworth
Boomer Esiason
Carl Pickens
Bob Trumpy
Eddie Edwards
Sam Wyche
Forrest Gregg
Andrew Whitworth
AJ Green
Geno Atkins

Just out of that list alone, you're talking 10 years worth of people added if only 2 per year.
If Marvin does get added, it won't be for another decade or more, most likely.
If the Bengals only do 2 people per year moving forward, they could end up continually having more deserving people ahead of Marvin as the years go by.