The Mets are currently interviewing first-base-coach candidates, and hope to finalize their entire coaching staff by next week. source Mets.com
So what do the Mets need, when they let Mookie go they lost their outfield instructor and base running coach. Although it may have been attributed to injuries the Mets weren't very aggressive 1st to 3rd under Mookie and haven't been since Rickey ( who I thought was over aggressive). It was specifically said that the team was unhappy with in game outfield positioning at times which was directly attributed to Mookie. If Riggleman were brought on he is a former outfielder and could take over the outfield responsibilities from the bench.
The other area to address is the catchers' coach, Jon Debus a former catcher himself was in charge of this area. While it was said that they wanted a pitching coach in the pen, it's also been mentioned that the team was concerned about Josh Thole's regression and Ronny Paulino's unwillingness at times to stick with a game plan. Bob Geren would be the obvious candidate to help the catchers and in a perfect world it would make sense to have Geren at 1b and Riggleman on the bench. While I'm sure Geren wasn't a speedster, the former catcher should have a feel for the batteries timing and the opposing catcher's arm.
If Riggleman and Geren bombed their interviews and the Mets did bring in Larry Bowa, they would have an entire staff of middle infielders, unless that mystery interview 1B coach was a former catcher who was a base stealing threat and moved to the outfield later in his career.
While it doesn't take a former player at that position to coach those specific skills, with the Mets admitting to positional problems in the outfield and game calling issues behind the plate; it would make the most sense to get the most knowledgeable instructors possible to address those deficiencies, which would probably mean a former player at those specific positions.