What are the upsides for Sony?It would end this negative press for a start, which would have lots of benefits. Would also make their gamers happier, since we can play with friends on other platforms, increase game sales on the playstation platform as people won't go elsewhere in order to have crossplay. They would avoid the danger of alienating some fans/ owners to other platforms next generation. Not to mention the extra revenue they could make from it if they make some sort of favourable deal with MS/ Nintendo. If they did it well and in a forward and positive way then they'd be receiving praise and positive press before the start of a new console cycle, which can only help.
If Sony wants to play the 'good guy' its a no-brainer. As it is right now, its just a terrible look and makes their claims of 'for the gamer' seem fake and unsupported, which they are of course, but they made it look true for a few years at least.