If people will be able to create their own commanders we will see even less diversity as there will only be enough room in the meta for 1-2 Commander archerypes per faction and everyone will use them.
See "Magic The Gathering Netdecking" for more details.
Hopefully it's implemented right. From the looks of it it seems like the abilities will be catogorized as such that you can't just choose any 5. But that probably won't stop people from finding the "optimal" builds.