Blood Magic vs. ES Reservation

The main (or even the only?) issue with Blood Magic (BM) currently is the drawback of not being able to use more than a single aura without severely cutting into your life pool. Therefore i'd like to discuss the possibility of using energy shield instead of mana/life reservation when and only when you have the BM keystone.

There are a few ways to do this that i can think of but those ideas mostly comes down to two options:
1. Change the BM support gem so it will apply the mana cost to ES instead when you already have the keystone:
+ ability to run several auras
+ more build diversity
- essentially free aura with just a few points of ES
- difficult to balance for low-life
To balance this, it would probably be necessary to disable the Mortal Conviction (MC) keystone for the ES reservation since the point is to be able to use only one extra 60% aura or equivalent without heavily specking into reduced mana reservation passives. Without MC this would be rather easy to balance if you consider the 196% reservation from the BM and 71% from a lvl 20 gem Reduced Mana support gem leading to 0.6 x 1.96 x 0.7 = 83.5% reservation.

2. Change one of the existing related keystones or introduce a new one located behind Mortal Conviction:
+ BM requirement already implied so the mechanic is more intuitive
[other benefits/drawbacks similar to above]
The keystone should probably have something like 80-90% less ES as an additional mod for two reasons:
a) so it can't be abused with low-life builds
b) you need to invest more into ES if you want to use this mechanic because of how the reserved values are rounded.

What do you guys think of these ideas and are there maybe basic problems that make it very hard to balance because of things that i overlooked?