Intel actually does do contract fab work - they just happen to be really bad at it so they don't get much business.
But there is a long tail of chip-making at older nodes to reduce cost, and for analogue integration. Risc-V is getting its start here. I hope we'll see a practical desktop version at some point, but that's not necessary for Risc-V to win.
Realistically, only Samsung, Intel, and TSMC can make next-generation chips. (Global Foundries just quit the 7nm race. They're going to be stuck at 12nm). Intel is fully proprietary tech, so that leaves Samsung and TSMC as the only companies that make chips for other companies.
At the end of the day, an open-source chip isn't really much benefit when there are only two manufacturers of chips.