Previously the tools would set direct = true unless the replica set name was specified, even if a seedlist was specified. As of go driver 1.4.0-beta2, this causes an error. This means any seedlist without replica set name causes tools to fail for tools 100.1.0+.
I think we should investigate if the direct connection was necessary - it seems weird to me that we would force a direct connection if a seedlist was specified. This seems to go against the expected SDAM behavior.
If we are okay with this change, we should at the very least change the documentation. The documentation currently makes it sound like specifying a replica set name is necessary to force a replica set connection. But a seedlist is sufficient.