Release cycles are not calendar cycles. It was 1.5 years between 5.1 to 5.2 and 4 months between 5.2 and 5.3. So the timing is not uncommon with a mature product. Major driving factors are Exchange versions and feature requests.
Please let us know if you have any questions regarding Archive Manager or any issues. We're currently working on the next release 5.4 and working on the release dates as well.
Thank you,
Dave
We are waiting for the 5.4 release as well and some news or ideas on release would be appreciated. We are looking to migrate to Exchange 2016 and some of the tools (like the "Archive Manager OWA Reconstruction Tool" are not supported.