a lot of people would probably make their own servers that probably wouldn't have many good qualities, just so they can feel "in control", and possibly brag..
less people would upgrade their accounts because it's harder to control what the server owners do (unless it's somehow linked with the master servers in a way that's hard to bypass, but even then it's still possible) .. this would probably depopulate the main servers more
there's also a greater chance of people disassembling/decompiling the server if they have easy access to it, and doing whatever they want with it (illegally) ..
even if there're ways around these things, it's not usually good to have players hosting servers that for the most part aren't reliable enough to want to link to
__
is there a good reason to have to host your own server unless
a) it's not good enough to be accepted officially
b) you want to allow playing for free
c) you want to modify the server illegally
?
NPC server doesn't count!

there's probably that could be made to test this in the client in the future, but I don't know if anyone will code it