First this is just speculation but now that Kimi has an offer from Toyota it appears that Yarno is on the outs there for sure. Kubicka stated when he signed with Renault that they wanted to team him with an experienced driver. It's difficult to think of a better choice than Trulli ('cept maybe Rubens). I would even say that Trulli and Kubicka have similar driving styles so they might make a good match up for the team.
In addition, qualifying will never be more important than next year when all the cars start on full fuel and there will be a lot more cars fighting to get in. Trulli is a great qualifier.