Hell no. I think its a bad idea and I don't believe in premium economy. At the end of the day it is still economy, just a bit more legroom. And as mentioned, it kills the Y-J upgrade option and will probably make J more expensive
It depends which airline we are talking about. There seems to be no real definition of what a PE product is, so we get this hotch-potch mix of airlines offering significantly differing products under the branding of PE.
If it is like BA 747 PE - why bother...rubbish product.
If it is like QF PE - then there is an argument for it. Food & drink very similar to J, and the seating is certainly a significant upgrade on Y seating.
If you can sell it also makes fabulous commercial sense, AFAIK PE passengers pay more per square foot of cabin than the other class options.
However for EK, PE might simply not be something worth considering. They can sell out Y, and appear to go pretty damn close in J and F. I question the value of a PE investment for EK on this basis.