Yeah a lot of the time the last thing someone who is acutely depressed needs is to be taken further away from their senses, I suspect sometimes ketamine itself can act as a useful cushion against reality in serious times of down, i.e suicidal etc, but only in those who are used to the drug.
In the IV ketamine trials it was titrated extremely slowly over hours, so not quite the same as a whacking great line up the nose.
Recreational drugs serve as useful exploratory models I think, but actual off the shelf medications need to be a lot more sensible to be useful....
edit> It's all round good news though that these trials are finally being conducted and the results are coming back positive, the glutamate system and NMDA antagonism has been the white elephant in the room when it comes to depression treatment for too long now, and finally some hard evidence is coming out that this is a potential new avenue to treating depression for the 21st century.