Is there any likely possibility to add support for IBM DB2?

I hope it does not sound to inappropriate to ask if IBM DB2 will be supported by nextcloud as a backend?

I’ve not heard of this before and the description of it on IBM’s site is somewhat vague. What value would this provide, assuming it was possible?

Nextcloud is a free softwrae (AGPL). I think nobody is interested to support a proprietary commercial database. Perhaps for money you find people to implement it. Ask IBM.

License Proprietary commercial software, Proprietary EULA

If you use a AGPL software like Nextcloud for collobaration there is no sense to use a proprietary database.

There are big installations (up to +500.000 users) with e.g. MariaDB and not IBM DB2. You do not need IBM DB2. Read PDF for scaling Nextcloud:

What is the reason for your question?

Likely needed for compliance with some kind of bloatage requirement, or someone in the organization got targeted by some slimeball salespeople to buy into db2 and now they need to justify it by using it for… something.