I've been hard at work for the last several months on a number of things related to MiniScript, including this website (with help from @hilbert), polishing up the C++ version, working on Mini Micro, etc. I also run a study in differential testing of the C++ and C# versions of MiniScript using Radamsa. The latter found about 16 defects, most of them just cosmetic differences between the two versions of Radamsa, but including a good half-dozen serious bugs that could be triggered by unusual inputs. So, that was a very useful exercise!
I'm going to start fixing those bugs today. I also have a handful of additional intrinsic functions I want to add; these are all things that have turned up in actual use to be very high-value, low-cost needs, like split and join.
Originally I had intended to do a minor release shortly after the 1.3 release at the start of March. But one thing led to another, and by now the list of release notes for the next release has gotten long enough to merit calling it 1.4.
So! I expect it will take maybe two weeks or so to wrap up everything I want to include in 1.4. I will then post an update to the Unity Asset (including the code editor), and open-source both the C++ and C# core code (not including the code editor). That will be version 1.4. Look for it sometime around the end of May, or mid-June at the latest.