Knowing how Woodie designed his class with various restrictions (only able to use the parts included in the kit that you were handed at the beginning of the semester, limited time to complete the project, etc.), I can see similar restrictions in FRC. Motor count is one of those. Restricting the number of motor controllers forces teams to make trade-offs. For example, choosing to use a swerve drivetrain with 8 motors (leaving only 8 other motor controllers for other things) is a tradeoff against a less motor-intensive drivebase leaving more motors available for other actions.
These are the kind of trade-offs that FRC forces teams to make which is part of the learning and part of the challenge.
I expect that FIRST will keep some sort of motor controller count restriction. I could see them increasing it over the current count, but overall, I think the GDC has a list of constraints they want to put in place for the teams to design within to make the challenge more challenging and motor controller count / PDP slot count is one of those constraints.