It's notable that the "meet the family" document IBM links from the press release — so we can assume it's officially blessed — says nothing about OMI, only DDR5 RAM. However, IBM has made it clear that Power11 will continue to have OMI, since enterprise Power10 customers would certainly have had an investment in it, and the upper tier datasheets reference OMI channel capacity. We don't know if the OMI firmware for Power11 is open and libre (it was not in Power10), nor if the Synopsys IP blocks reportedly used in Power10's I/O are still present, because IBM didn't say, or if the "low-end" binned CPUs are different in this regard.
If there are going to be third-party Power11 systems, and IBM didn't say anything in the press release about them either, they generally follow six to twelve months after. We have heard little from Raptor since about the SolidSilicon S1 and X1, and because all indications suggest the S1 is a Power10 implementation without the crap, this already puts them behind the curve. That said, adapting Power11 should be possible to any next-generation Power ISA workstation: the Talos II and T2 Lite are fairly straightforward reworks of the reference POWER9 Romulus design, and Blackbird is still Romulus, just in a much smaller form factor. These first-generation P11 boxes, as presumably performant as they are, wouldn't be nice to have in an office and IBM just doesn't do end user sales. Creating a T3 based on Blueridge would seem to be the best way forward for Raptor to regain the top slot in OpenPOWER workstations — assuming the architecture is still open.
[UPDATE: I have been advised by an anonymous individual with knowledge of the situation that a new Raptor announcement on products under development is scheduled for Q1 2026 ... which would be "six to twelve months after" as predicted. "Open firmware" is specifically mentioned and absolutely planned. It's worth pointing out that both Raptor and SolidSilicon are now listed as top-tier Platinum members for OpenPOWER parallel with IBM itself. That implies SolidSilicon is still in the mix and IBM is still backing OpenPOWER. They stressed this is not an official announcement, so you take it for what it's worth.]