It was basically a freemium model, which means that a complete OSS solution is out of reach.
This basically looks like the same thing. I guess Hashicorp is slightly better at OSS, but... I dunno.
A DMS needs:
1) storage (duh)
2) metadata
3) permissions enforcement
4) search / indexing
5) rendering to pdf and pdf signing services
6) workflow engine for document lifecycles, versioning, approvals, rendering
7) a bunch of virtual filesystem interfaces like CMIS, maybe JCR, webDAV, SFTP
8) a decent web client
9) a decent integration API
It's quite the laundry list. A "modern" one should probably be cloud-aware (so docs can be stored in cloud object stores, utilize interface with the various semi-document features of S3 or other object stores, etc.
IMO it should also be implemented perhaps as a non-cloud self-hosted option atop Cassandra or some other scheme with good global replication and scale.
Honestly I don't understand why a consortium of governments and businesses with high regulatory requirements don't simply get together and develop a common platform for this. They'd rather give billions of dollars to Documentum or Oracle. If they want support, SOMEONE will provide paid support, like Postgres