With the creation of branch 5.3, the master branch is again open for adding new features, to be part of future release series v5.4.x.
Based on the workflow used during the past years, the next future release v5.4.0 should be out after another 8-10 months of development, plus 1-2 months of testing, so sometime in close to the end of spring 2020 or afterwards.
Thanks for flying Kamailio!