Why should Keaschall have to wait for an injury to occur if he outperforms any of Julien, Lee, Miranda and/or even Lewis in ST? If he's going to sit on the bench, no, start him at AA or AAA. But if he earns a spot, give it to him.
And yes, I understand that many teams try to manipulate playing time to keep that extra year of service time, so even if he earns it, he may not be up until sometime around May 1.