I haven't heard anything about this. I'm currently using MDAC to protect my PC, too bad if Microsoft is going to stop develop this feature without anything to replace it.
Microsoft more often than not slows or ceases development and then makes no comment. For example, does anyone remember PowerShell Desired State Configuration (DSC)? For a couple of years Microsoft promoted it hard. Then after a few years Microsoft just stopped talking about DSC. Now DSC resides in the realm of projects Microsoft started, but has not finished. Oh Microsoft has online documentation for DSC, and it lists that it is "still in development," but when you start to dig around and ask Microsoft questions about the current state of DSC and its future there is nothing but silence. This sort of behavior from Microsoft has been a part of all things PowerShell since 1.0 and it is just not limited to PoSh. The same Microsoft behavior applies to AppLocker, SRP, MDAC (WDAC), and others. Lots of things Microsoft brings to market ultimately just "fade away." AppLocker is a good example. Microsoft still ships it with Windows images, but there is no work being done on AppLocker.
MS works on these kinds of features in small teams. Sometimes key personnel will leave Microsoft and then the project will stagnate for a long time - sometimes years. Other times, these small teams do not coordinate among themselves very well. The result is very slow progress. It is a good bet that the slow progress of WDAC is due to such internal issues or logistics.
You can search for MDAC release notes, but you will not find much of anything (that is significant) within the past 5 years. Microsoft certainly has not made WDAC a top priority to refine in order to make it a serious, user-friendly, practical replacement for SRP, AppLocker, Configurable Code Integrity (CCI - the forerunner of WDAC), and so on.
If the good folks at SANS have dropped teaching MDAC (WDAC), it is a pretty good indication that it is a stagnant Windows feature. They have deep contacts within Microsoft and are in a position to know I asked Jason Flossen at SANS why he no longer taught WDAC, and his reply was basically "WDAC is a dead duck."