Well, I suppose every "source available" software in our world would automatically become free software in that world (I'm assuming any other pseudo-copyright bullshit will not be a thing in that world as well, patents, weird trademark clauses, special legislation for DRMs, etc). And I think the incentive would be as large as the incentive to make "source available" software in our world, so yes, but I think for your question this answer would actually be "no". If I am a developer who only releases binaries to, idk, make sure you pay me to give you updates, I would keep doing that doubly so in a no-copyright world, except I'd also probably invest into tools that make reverse engineering harder.

CC: @eric@pl.starnix.network @Suiseiseki@freesoftwareextremist.com @maija@netzsphaere.xyz