I think they should play him when he is eligible to come off the IR, try to build some trade value, but I don't think they will, unless Jacoby goes off the rails, even then...
I think there is some fire behind the smoke. They told him that he was going to backup Jacoby and I think Kyler said "nope, if that is the case I am done". The rest is all just cover to retain some trade value.
I don't see any other explanation for him to go from day to day and practicing to "out 4-8 weeks".
I know he's your guy, but after that Rams playoff game, where they had to talk him into suiting up for the 2nd half... I think he's never faced much adversity as an athlete and when it hits him hard he quits.
Now that were out of the playoff picture, I agree it makes sense to play Murray once he's off IR. Like you said, even if he just plays mid, it will help his trade value in a QB-starved league.
It will also function as his last stand in ARZ. One final chance to prove he can at least be above league average (10-15 range).
And after his stint on the bench, I have a small amount of hope he'll play better.