Dear ven, that is fantastic, thank you so much. I have made a ticket for this and we will add the updated font.
Normally we use Google’s Noto fonts for scripts not covered by our main font, Skolar. While Noto may not be the best designed font in each and every case, it has consistent style and metrics, so we can use many different scripts on the same site. Another advantage of the Noto fonts is that they come in many different styles—serif and sans serif, different weights, etc.—allowing for complex typography.
The extra 15 characters have not been added to Noto, but the issue is noted, and they are planned to be added in “Phase IV” of their development cycle.
This will take some time, however. They are currently 60% finished with Phase II, so we can safely say that Phase IV will be some years away.
So what I am wondering is, might it be possible for you to add the extra 15 characters to Noto? The license allows reuse with modification, so that is not a problem.
I have compared the metrics of Lanexang Mon4 (red) and Noto (blue.
As you can see, they are quite similar in weight and x-height. The line-height is a little different, but not too much.