True on livestatus and Nagios 4 support issue, I had to use livestatus-1.2.6 for nagioscore 4.
CRE-only will require big nrpe to checkmk agents migration effort and checkmk UI need some orientation effort.
I like CRE can connect to existing nagioscore+livestatus instances without big changes.
I am exploring the possibility of very slow migration over to CRE-only at our own pace.
Using CRE as central dashboard for all nagios instances is an OK starting goal for me.
BTW, can your company consider to provide CRE commercial support ?
Nagios provide nagioscore support also.