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.
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.
It does not compete with its clients who produce chips.
Thus anyone with a contract with TSMC can be a chip producer.
OpenPOWER is basically a set of documents and specifications that is analogous to IBM's original "PC" specification. This is good for sure, but it doesn't mean that POWER9 is open source like RISC-V is.
If anything, I think OpenPOWER is a good example of why an open-source chip is unnecessary. It shows that a group of companies can work together and build a major platform without the need of open sourcing the chip. I'm unsure what RISC-V gains above and beyond the OpenPOWER consortium.
So we the typical user can't make use of open source designs.
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An open source "conglomerate" of companies may work. But I haven't fully thought about the economics of it.