Thank you! Nice list!
If I could add ONLY ONE thing of most things not on this list that I think we need most, it would be changes to terrain / the playfield.
The Map, Terrain, and Movement. In GC2, one main shortcoming was the uniform map, due mostly to its space theme setting -- there were no terrain variations which yielded strategic choices (e.g. chokepoints e.g. pathing decisions). I feel that Elemental is not much better. In most other games of this genre, attention to the map and its features is key, for many reasons; in Elemental, one need mostly look at the "glowing bits", and treat the rest as a relatively uniform, if cosmetically varied, surface. Why? Two factors. Factor one: Terrain features (grassland, forest, swamp, hills, etc.) do not appear to play a significant factor in modifying a unit's movement, nor do they play a significant factor in any other aspect of the game except for defensive bonuses (whose exact workings are unclear). Factor two: Most units in Elemental move at a uniform speed, and most apparently do not have flags for being affected by terrain. This is different in most other land-based strategy games, and for good reason: they give the player options in making interesting strategic choices. Because Elemental lacks these in this context, it becomes, in my opinion, that much more lackluster.
In games like Civilization or Dominions, it matters a lot which terrain tiles (e.g. jungle or swamp, grasslands or hills, etc.) are in your zone of control; in Elemental, it doesn't seem to matter at all. In fact, the only real use for zone of control that I can see is that it lets you own shards. Thus Elemental's map is very much like GC2's: a wide open, uniform field, whose sole characteristics were "resources" (shards). As I tried to describe in my post from August 2006, this detracts from the game's strategic elements and makes it less fun.
(1) Make terrain (and not merely terrain enhancements, such as fertile land) matter to economy, city building, questing, neutral spawning, and the chance of yielding special events, e.g. hills will have a greater chance of harboring metals but will rarely yield food. This might require reworking the resources system (e.g. making resource requirements and units of measurement larger and more dispersed). By that I mean it might make it easier to count if "food" increments were increased by 10, so that for example a hut required 10 food, and so on; I would suggest making farms provide 20 food (or 2 food in the current system) and letting grassland tiles provide 0.25 food (or less in the old system), forest tiles provide 0.25 materials, hills provide 0.25 metal, and swamps provide a slight chance of something interesting to spawn. One could also imagine that with the correct technological advancements (e.g. in civilization or adventuring), one could glean additional boni, e.g. with hills, there might be a chance of finding "caves" if Adventure Level X is unlocked, etc., while plain grassland should yield an additional slight food bonus...
(2) Give movement bonuses (for certain units) on certain terrain types and penalties on others. This should apply predominately to the strategic map, but also to the tactical map. On the tactical map, terrain should also affect LOS for ranged attacks and fog of war. Age of Wonders did ok with this many years ago.
(3) Make terrain interactable not only with units and the economy, but with spells, for example summons (Treant only on forests), buffing (Camoflauge only in hills), damage (Avalanche only in mountains, Quicksand only in swamps), or in general (buff on a champion lasts X turns, gives all units under that champion's control +1 to attack for each point of charisma that champion has over 9, but +2 points per Charisma over 9 in forests), etc.