As of today galera has an arbiter solution to preserve quorum in case of network issues.
Role of the garbd (aka galera arbitrator daemon) :
be part of the quorum to try and preserve it
relay proxy for galera messages

aas of today the garbd is just the wsrep plugin ( see there https://galeracluster.com/library/documentation/architecture.html)
with plugs so that it always happily certifies anything instantly.

moving it to maxscale monitor would provide maxscale with powerfull integration into galera cluster and would totally make sense.

Since maxscale usually runs into the same DCs as galera nodes, we could just make a direct port with some tweaks to provide informations to the monitor.
Yet the best integration would be : having codership separating the replication traffic from the quorum calculation traffic in some way. tahtwould mean we could have a quorum member that doesnt replicate. it could even lead to garbd like piecs of software using vrrp or consul for automatic topology management.

i will add some design schemas in the coming days.