Full disclaimer: I have no exclusive knowledge about the design points the devs are already working towards, but rather I'm basing this off of thoughts I had while modding in Warframe and how they relate to similar limitations with how CoX handled enhancements. The devs may have already considered these points.
The main aspect of what I want to bring up is that not all enhancements/mods/augments/whatever are created equal, and certain types of mod will be almost always disregarded if certain other types of mods are available.
Specifically, the vast majority of enhancements available in CoX (for common point of reference) enhanced any give aspect at a fixed percentage (33% for Single Origin enhancements, IIRC, but the specific value is largely irrelevant), but this was a mistake because of how different enhancements affected the abstract qualities of the Powers. I posit that these abstract qualities are Efficacy, Efficiency, and Consistency. Some enhancements would, by their nature, either only one or more than one abstract quality, making them inherently more desirable when the enhancements provide the same mathematical bonus.
For example there is the power "Fireball". There were several standard types of enhancement that could be hypothetically slotted in Fireball. Damage, Accuracy, Cooldown, Endurance Cost, and Range come to the top of my mind (feel free to remind me of others, not counting special drops and set bonuses). However, in practice, the optimal build would exclusively slot Damage and Accuracy enhancements, with a heavy skew in favor of Power. Why?
Because these enhancements improved at least two of the abstract qualities. Damage enhancements obviously improved efficacy (Damage per Second), but also improved Efficiency (Damage per Cast Time and Damage per Endurance). Accuracy enhancements enhanced all three qualities, but with a practical hard-cap of not being able to reduce the miss-rate below 0 (or any coded hard cap for accuracy). The other available enhancements, by contrast either only provide a bonus to one quality. Cooldown reduction hypothetically improves efficacy, but not efficiency, and not once a consistent power rotation is developed. Endurance cost reduction help efficiency, but not efficacy. Range arguably improves consistency in relatively niche applications, but does nothing for efficacy. This kind of design issue was prevalent across most powers in CoX. You'd slot a power with either only one type of enhancement, or at most predominantly 1 enhancement with an odd enhancement out (usually accuracy).
How can this sort of design rut be avoided? There are a few ways I have seen it done:
1) CoX eventually implemented Enhancement Diversification, which caused repeated instances of enhancements providing diminishing returns. IMO this largely failed to achieve its goal because it didn't consider the fundamental design flaw that causes players to 5-1 or 4-2 Damage-Accuracy and disregard other enhancements.
2) Warfame makes it mechanically impossible to slot repeat instances of the same enhancments (mods in that game's jargon). This does better, but the end result is more that a few slots are reserved for a very consistent collection of mods (Mainly those that directly enhance damage per shot), and a couple of slots that only change to modify the elemental type of damage the player wants to use. In practice, while there is more variation than we saw in CoX, the actual avenues for players to find niche applications via customization seems less than it might be.
3) The apparent path that CoT is going is to have different slot-types for different enhancements, which is in a "the jury is out" status until the game is released (obviously)
I have a few ideas relating to how to actually design the CoX enhancements, some of which are mutually exclusive, and should very much be considered "spitballing" ideas.
A) Do not include enhancements that directly affect efficacy (EG: Damage enhancements). Instead, the powers either automatically scale with character level, or adding the slots provides an automatic bonus to efficacy/accuracy. This is probably the most controversial option as most players will generally assume that they will be able to add Efficacy enhancements to their powers. However, this leaves the slots open for more interesting variation in build (Cooldown Reduction based burst damage vs Efficiency based sustained damage, for example)
B) Efficacy enhancements include a drawback. For example: Damage enhancements increase stamina cost or cooldown, or reduce accuracy. This idea is probably the most volatile from a design perspective and would probably eat more development time as a proper balance is found that keeps things fun without players being able to break the crap out of it. I personally think this would be the most interesting, but I'm also sure the Devs have enough work on their plate as is.
C) Efficacy enhancements are mathematically weaker than their counterparts. Optimal slotting becomes less clear/more situational when you need to decide between a 33% cooldown reduction enhancement vs a 20% damage enhancement compared to a 33% cooldown enhancement vs at 33% damaged enhancement. This is probably the most straightforward and easiest means of addressing the issue, but IMO is still the least interesting (other than how CoX handled it).
Thoughts? Criticisms? Inspiration?
Sic Semper Tyrannis