We internally compiled a list of standards, and I'm now moving these to a page on meta.wikimedia.org (currently preparing in my userspace):
https://meta.wikimedia.org/wiki/User:SandraF_(WMF)/GLAM_metadata_standards_inventory

The idea is that this will become a list that can be enhanced, extended and updated by the community.

I have now moved the list to mainspace on meta.wikimedia.org and extended it quite a bit. Still more to add, but we're slowly getting somewhere:
https://meta.wikimedia.org/wiki/GLAM/Metadata_standards_and_Wikimedia

This list and initiative has also been mentioned in the This Month in GLAM newsletter of May 2020:
https://outreach.wikimedia.org/wiki/GLAM/Newsletter/May_2020/Contents/WMF_GLAM_report

As a next step I want to socialize this list a bit more broadly with the GLAM-Wiki community, asking for input. My hope is that the page will be maintained and extended by the community, going forward.

@SandraF_WMF Would it be helpful if I spread the word also via my channels?

In T249690#6200455, @David_Haskiya_WMSE wrote:

@SandraF_WMF Would it be helpful if I spread the word also via my channels?

That would certainly be welcome. Thanks :-)