Making it not mandatory would break most of the important functionality of the module, so its not really an option.
Yes, you can segment inside a list, and still can. But like I mentioned, lists should be used for channels. There is a difference in channel from someone that automatically comes over from your shop and someone you are wanting to add manually.
Like some of our lists are :
from 40 nuggets
forum users
shops that have been migrated
new installations
ect.
They are different channels, with different purposes.