When it comes to desktop environments, having several options is a good thing. I like the idea of having different desktop environments available, because it give the users a choice about which one to use.
No two people work the same, or have the same way of doing things, so being able to select a desktop environment that better fits the way the user does things is a good thing have. Not only that, it gives the user, and distros, the option to change to another one if the desktop environment developers take a road that they disagree with.
At the end, it's a good thing to have since it means that people are free to choose what fits better.
The desktop environment should shouldn't get in the way of the user's work flow as it can. It should be almost unnoticeable to the user as it can be, as if it isn't there as all.
One size doesn't fit all, and user's shouldn't be forces to accept a desktop environment just because someone else says they have to. User's should have the freedom to select what desktop environment works for them, and their choices shouldn't be limited by any one else.
A desktop environment success should be determined by how many users adopt it because they like it, and want to use it, not because it was forced to them to use.
If users flock to 2-3 desktop environments, that good. Let the users be the ones who determine which ones survive, and how many of them can co-exist in the market.