From what I remember reading about the first all-stars, the producers were desperate to have some kind of crossover team regardless. They tried for Flo and Drew, tried Brennan and Emily, etc, and eventually settled on Eric and Danielle after others declined. So I dont think Colin and Christie would have bumped them out if they had taken part in TAR11. More likely they would have bumped someone like John Vito and Jill, who were last minute alternates as it was.
As for TAR31, I think the cast could have been so much worse given the gimmick. It looks like they tried to stay close to TAR's usual type-casting, even with the gimmick (married couple, sisters, moms, etc). So the cast we ended up with is far better than it could have been based on those rumors. On the downside, maybe not getting all the dramatic personalities CBS originally wanted hurt TAR31's scheduling, causing it to get bumped to summer. Just speculating.