Hi @finnian,
I like to think of mead as an opportunity to create a tincture. This is because the mead, just as with any other alcohol-based preparation, will extract more of the active medicinal components than a simple water-based preparation. This being the case, any herbs which are commonly prepared in tincture form can also be prepared as a mead. You'll have to tinker to get the proper flavor balance, but Siberian Ginseng (Eleuthrococcus, 五加皮) might be a good place to start. You might also try Goji Berries (枸杞子) or Shu Di Huang  (熟地黃), as these would potentiate the ferment itself. In a forthcoming post (this coming week), I'll add a classical recipe for an alcoholic beverage made from a combination of the two. 

In any case, I recommend you try a tea (decoction in water) of any herb before you take the time to prepare it as a mead. No point in putting the time in if you don't like the flavor ;)