We are approaching the end of this beta-testing and the new version is working very well with WP 5.1. We will soon include this as a standard feature in a forthcoming revision.
In itself, this DOS compatibility was not a goal we felt worth pursuing as it is a dwindling market and most users already have an expander solution. But it came almost for free as a result of extensions we did for multi-threaded applications and we felt it would help IT users who occasionally work for an account that requires WP 5.1 or some other DOS application.
Jean Ichbiah