Rasheed Wallace is a good call. I know it's a Simmons rip-off, but Sam Cassell could definitely do it. When I think of possible future coaches I think of second level guards, like Lenny Wilkins, Doc, Ainge, Mo Cheeks and Avery Johnson. Guys like that who come to mind are Derrick Fisher, Steve Blake, and Chauncy Billups (although he's definitely better then second level).
First, I agree with your premise that guards are the place to look when looking for future coaches and you can narrow that down further by saying guards that were good because of their BBIQ.
Example: I think MJ, Vince Carter, and Tracey McGrady are more athletic basketball players first and mental basketball players second. I think they would all suck as coaches.
Ray Allen, the aforementioned Eric Snow, Andre Miller, these are guys that bring a calmness to the game, that can communicate very well and see the game, if you know what I mean.
Second, I think you owe lenny Wilkens and Maurice Cheeks apologies for calling them second level guards.
Lenny Wilkens
Hall of Fame - 1989 as a player
9-time All Star
All-Star game MVP - 1971
Twice NBA in Total Assists - 1970,1972
Led NBA in Assists/Game - 1970
10 straight years in Top 10 Assists/Game
7 straight years in Top 3 Assists/Game
Runner up MVP 1970
Voted NBA Top 50 Player Ever
Maurice Cheeks
4-Time All-Star
4-Time NBA All-Defensive 1st Team
1-Time NBA All-Defensive 2nd Team
10 straight years Top 10 Steals/Game
8th All-Time Steals/Game Career - 2.1
4th Alt Time Total Steals
Widely acknowledged as one of the best defensive PGs ever