It seems really odd to me that they are changing to an 8MB limit. "Document storage database" that can only hold 8MB per document. It can't hold full text output for a large documents... What am I missing here?
In CouchDB 4.0 the backend of CouchDB will be switching to FoundationDB, which will have a 8MB limit, so they're preemptively making the change. You can remove the limit now if you'd like.
FoundationDB needs is a consistent (as per CAP) database, to make that work in a distributed fashion, there are limits on distributed transactions in size and time. CouchDB needs to adopt those in order to move to FoundationDB.
The 3.x series will be supported for a long time for folks who can’t move up. Until then, as others have stated, you can up the default limit.