Over the last week or two I've been playing through Diablo 3 again with a Necromancer, and I had the exact same experience that I did when I first played it five years ago: within an hour I had the same skill loadout that I would use for the rest of the game. New stuff kept unlocking and it didn't matter because what I already had was just as good. From then on all that mattered was swapping in the equipment that made my stats bigger.
This happens a lot in RPGs and it's always disappointing; you're given a seemingly infinite variety of ability combinations, yet other than your own curiosity, there's no impetus to try anything new. It shouldn't ever be the player's responsibility to provide variety to a repetitive game experience. From the very beginning of Silicon Void's prototype phase I wanted to find a creative solution to this problem.
Rather than punish players for sticking to the same play style, I wanted to incentivize frequent voluntary changes. What I eventually settled on after much iteration is a system that requires alternately equipping and unequipping Abilities to unlock their higher power levels. Each copy of an Ability earns XP individually while equipped to one of the player's frames, until it reaches a certain threshold. In order to continue earning XP, that Ability must be moved to a development slot in your loadout. Once the next XP threshold is met, the Ability levels up, and will stop earning XP until it is re-equipped, at which point the cycle repeats. Leveling up not only makes the Ability's effect more powerful, but also increases the passive stat bonuses it grants to the frame that equips it.
It took a few tries to get this feeling right. One of the mistakes I made at first was having the XP requirement for the unequipped phase of each level be larger than that for the equipped phase; in hindsight it seems obvious that such an arrangement would cause a permanent bottleneck of Abilities waiting to be developed. Currently the unequipped XP threshold is 1/2 that of the equipped threshold, which seems to be working well enough at this early stage of balancing.
It was also hard to account for the early game, when the player would have few Abilities total and unequipping one would be a huge drag. That was alleviated by the introduction of "attached" Abilities that are built in to the frames; they don't earn XP and will always be a low level, but the player doesn't have to think about managing them. (Credit where due - I tried this out after remembering a similar system at work in the FF13 sequel Lightning Returns, a game with a lot of weird ideas that definitely merits its own blog post someday.)
Abilities also each have their own cap on the number of copies you can hold in your inventory. For staple Abilities like heals and elemental attacks, which are much too fundamental to give up entirely for several battles, the cap is 3. Specialized effects - for instance Rewind and Fast Forward, which move the turn clock effect in either direction - are limited to 1, as these are exactly the kind of combo-oriented Abilities that I wanted to discourage the player from relying on permanently.
Eventually each Ability earns a maximum level; without the capacity for further development, there is no longer an incentive to swap it out. On top of that, better Abilities will come along that eventually render even the fully developed versions of early abilities obsolete. For those reasons, a mid-game system will eventually unlock that lets you sell maxed-out Abilities for upgrade points that are spent on permanent improvements to the party. Normally these upgrade points are earned very slowly, so sacrificing Abilities will be necessary to afford the really expensive perks - including increased XP and currency gains from battle, and more development slots to power up more Abilities at once.
That system is one of the many additions to Silicon Void which you can expect if the game is funded on Kickstarter, and the campaign is coming Real Soon! Thanks for reading!