Has DocuWare looked into supporting PostgreSQL? It is an open source product that is quickly overtaking Oracle as a the big guy on the block. Can manage as many users as you want and PETABYTES of data.
There are also features within the product supports a multitude of sophisticated query, index, partitioning of tables and Isolations as well as JIT, Parallelization of reads and indexing. Suuports PITR actively and security authentication can be as complicated as you want. Supports procedural language like PGSQL. Perl, Python etc, supports foreign data wrapping to connect to other datasbases or streams using the SQL standard. Great Documentation, with 30 years of dev behind it, Postgre looks prime to take over a large amount of SQL space in the market.