Even in the absence of copyright allowing one to sell licenses in the traditional sense, if the software is worth having then it seems that there should be someone(s) who will pay for it.
This is kind of self-obvious because absence of copyright will only affect tiny slice of the software: 10% (if even that!).
If you are paid to write piece of Facebook or Twitter then you can not distribute source not because it's copyrighted but because your contract includes the NDA (which means that you can not even distribute some numbers which are thoroughly uncopyrightable).
And from said tiny slice a lot of projects can be financed in kickstarter-like model. Companies donate code to Android not because they are receiving royalty!
I don't know if Redhat is the exception that proves the rule or a demonstration that you can still charge money and do well without using the traditional copy rights.
RedHat is an exception because of existence of copyright. Government spends taxpayers money to enforce copyright while any other model will need to find all the resources "inside" which of course will make it less effective. In the absence of copyright there will be more kickstarter-like activity, donations and other such things.
This does not mean full abandonment of copyright is a good idea. But it's good idea to compare disastrous consequences of it's enforcement (absolute lack of privacy for one if person-to-person copying is considered illegal) with it's benefits.
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