In the aftermath of
WT-4029 we (Michael Cahill, Daniel Gottlieb Keith Bostic Maria van Keulen) discussed ways to move forward in the future such that an older binary can detect a future binary has run.
The executive summary is that the easiest path forward is for WiredTiger to store the current compatibility version every time it is set, such as startup or when it is modified, in an unstructured file. Where is not yet determined. It could be a limited version of WiredTiger.basecfg or a WiredTiger.version file or something new in the turtle file.
We should try to get this in for 4.0.0 so that the support is in there going forward ASAP.