The current design is too limiting and slingshots you into a very awkward play style to maximize your leader’s value.
However what you're proposing is probably worst because the passive enters in direct confrontation with the order, the order requires you to have a hand full of units to maximize its value which won't work if you have to include Nature cards in your deck for the passive. Furthermore, there aren't enough Nature cards to justify such abilities, and some Nature cards such as Water don't really make sense in a hand buff deck.
I'd rather see something around the lines of "Boost a unit in your hand by 1. Charge: 8. (Provision 16)", which would bring a much needed flexibility to the ability, or even "Boost a unit in your hand by 1. Cooldown: 2. (Provision 17)" if you fear stacking boosts.
It’d represent at best 19 points with Skaggs if you decide to use all charges on one card, which isn't what I'd recommend to do, and even then it looks somewhat fine compared to the 20 points that Dagur + Reckless Fury represents, even though Skaggs has a harder removal value. It's also only 18 proactive points with Aglais. In any cases you most likely wouldn't use all your charges on one card because you might want to hand buff others (Mahakam Defenders, Wardancer, Schirru, ...), and the hand buff archetype might, and should, get more cards in the future promoting a greater spread of boosts in your hand.