My understanding is that you can have a three node active:active:active RDQM environment supported by one full MQ Advanced license and two HA replica (20% cost) MQ Advanced licenses. So effectively 1.4 licenses for 3 nodes. Obviously you need to allow some headroom to run 2/3 queue managers on one node in a failure scenario, but the licensing is much more favourable than multi-instance (where HA replica licenses only apply to passive queue managers, and full licenses apply to all active queue managers).
Points to note - no support for RDQM in containers therefore not for use when deploying in containers in ICP4I - but can be used outside. Also RDQM for MQ is not supported currently in use with ACE/IIB - therefore that isn't something to consider.