Gave the new MegaMek a whirl last night.
Did a quick map to see if there is any changes in Map Editor.
Selected my forces, love the UI, but when I went to the Map Tab that is when things went south.
It appears that there is no way to load a custom map from the boards folder in this tab. Left and right clicked everything. Looked through documentation, all to no avail.
Is it possible that feature is not yet implemented in the beta and I missed that announcement?