If Solaris source had always been available under the GPL, it would have removed the incentive for Oracle-Sun to sue other people for announcing support for OpenSolaris or RedSolaris, or whatever. Of course they might have done that anyway, but in 2020 they would have been more likely to donate it to the Apache Foundation or something. Or we could have had the competing Solaris Foundation, promoting its Sun-centric technologies like dtrace, zones, and zfs as first-class alternatives to the corresponding Linux technologies.
Obvious disclaimers: Not a lawyer and not necessary good at predicting alternate futures :)