I think it could make sense to extend the Eglinton LRT even further west to at least Dixie road to serve the offices around there. I'm not sure if it would have to continue back from Pearson or branch at Renforth. However, that adds even more KM to the extension, making it seem even more cost effective to do it at grade to me.
If it doesn't happen, then going to the airport offices requires transferring to a bus at Renforth, which could be inconvenient.
My main concern with elevated is that cost reduces the probability that it will happen any time soon (politically), and that elevated doesn't really buy you much anyways since there aren't too many traffic lights along the route. Also, the EA is done at grade already so I think that would save years of time for the at-grade option.
Having said that, I have no problem with elevated or trenched if it can be done.