Not a good idea in my opinion. All it does is make MoM a pretty much mandatory option if you were to take EB, which kinda negates the initial purpose of EB, which was to allow ppl to run a higher number of auras (which has gotten nerfed by the % changes anyway) and to increase mama regen. At this point, I'm sure there are still ppl who choose EB without choosing MoM, so all this change will do is further limit build variety.
If a nerf is needed, a simpler solution would be to just change EB to 50% of ES converted to mana, leaving the player with some ES to protect life, while also promoting mana regen and at the same time making MoM less of an automatic choice for EB users. Another option would be to just have a 20% less ES modifier on the keystone. No need or change things too drastically. MoM should be balanced around EB, not vice versa