In the case where I would consider "Energy Shield", I would make it similar but more like this now that i've thought about it for a moment.
Before you read this, consider that this is what would replace Worker Hit Point Upgrades.


Energy Shield (4 levels)
Creates a shield made of mana to protect the workers. The shield takes 1 damage per mana point and provides +30 mana for each research level.
Lumber Cost: 350 + 150
Gold Cost: 0 + 0
Requirements:
Level 1: , 350 Lumber
Level 2: , 500 Lumber
Level 3: Merchant, 650 Lumber
Level 4: Merchant, 800 Lumber
Quite frankly what happens is that Energy Shield would replace the Worker hit point upgrades and instead put this in. The result is that Draenei workers although can only build up 200 hit points (Nuke perspective) in total, they can acquire it earlier than any worker and thus gain a weak form of resistance against nukes. A great way to present them with an option to seed, since the shelter centered food structure already promotes that.
The downside is that nukes that deal more than 150 damage are going to overpower even the "150 nuke perspective hit points" pre-merchant.


Champion Workers
Panda:
- Champion Workers, Magical Resistance removed.
Arachnid:
- Champion Workers attack damage removed.
- Champion Workers Hit points reduced from 250 to 75.
- Champion Workers receive Burrow:
Burrows the worker in place, giving it 75% magic resistance but renders it unable to move or harvest lumber. While burrowed, the Champion worker has +100% hit point regeneration.
This change practically kills the comfort Champion Workers have of not being nuked early. Apart from Succubus that still will have hit points to survive an unspecialized nuke, it will put more vulnerability to them. Arguably, this makes them much more situational since there is no massive hit points to them that you can rely on.
But it also makes them more of what a worker could and should be. They were made I believe to be space conserving alternatives, not a luxury meant to take away from the little action there is.
You never see a titan nuke certain seeds that happen to have champion workers and I believe that is wrong. Dead wrong because Champion workers should really differ in usage of space, not awesomeness of Titan deterring hit points.
Feel free to promote or reject these two changes.