I intend to re-implement a feature of GAE that I believe was useful: tags.
Tags are just a label (or multiple labels) that can be given to a unit type. Then we can make changes that only apply to units that have certain tags. For example, instead of listing all the units that an upgrade is applied to, we could instead use tags to assign some custom property (eg, "warrior" or "mage") and then apply the upgrade to all units with that property. These are more useful with attack boosts, since attack boosts can affect multiple factions.
Tags are most effective if they are used consistently throughout the entire techtree. They make it easy to apply attack boosts to a group of units based on some property (such as whether they're a building, a sword user, etc).
Tags also have future potential in being used with other features. For example, looting could be improved by assigning a list of tags for units that can loot (perhaps normal units can loot, but buildings (like the defense tower) cannot). In fact, I intend to extend looting in this way after tags are implemented.
I intend to use the same syntax as
GAE did. As an aside, the feature does seem redundant when first using it, but it's actually quite a please to use (speaking from experience) when used consistently throughout the techtree. It works best for mods that use attack-boosts (emanations in GAE) heavily. It's a pain in the ass to keep adding units to the various affects lists of attack-boosts every time you create a unit. Easier to add a tag in one spot.
For a real example of how a tag is useful, consider some zombie warrior that inflicts a disease (using an attack boost) on nearby units (in GAE, this would be better done with an
effect, which is essentially an attack boost that is applied to the target of an attack). Anyway, it doesn't make sense to apply a disease to a building, so naturally we're going to limit this attack boost to only effect humanoid units. How do we do this? Do we keep an affects-list of every humanoid unit in this attack boost (and bear in mind we have to manage all these affects-lists)? Tags provide an alternative by simply saying that the attack boost affects "humanoids", and then each humanoid can be given a "humanoid" tag. Thus, we localize the unit properties (being humanoid) to the location that they are relevant.
It's going to be a few days (or perhaps until the weekend) until I can get started with this, so feel free to discuss this idea.