I don't have the benefit of being at Training Camp, and have to rely on what has been reported. From all accounts I have not heard of anything suggesting that Yates play on the field has distanced himself from Case.
That being the case, I don't see why it is such a stretch to entertain the thought that Case might win the backup job.
Texans_Chick seems to suggest that there is no possibility of this occurring. I read her blog and her reasons why. I understand that Case has practice squad eligibility and Yates does not. But I have still yet to hear any accounts that Yates play is significantly better than Keenum's so far this year.
This will all play out soon enough, and Yates may be the best QB for the job, but I don't think it's unreasonable to not count out Case Keenum.