Hey there! ^-^
I’d like to mention a concept I’ve been thinking about for a while now. I’ve come to call the concept “mutators” - I’m not sure it’s a great name, but I couldn’t think of a better one, and now I’m used to it, so it is what it is :')
The idea came from the fact that there are skill modifications that would fit in a skill tree as a node, but would be quality-of-life features, or customization purely based on player preference, without providing any form of power to the skill, which would make them feel not “worth” spending points in, when those points could be spent to actually gain skill power.
A few such nodes are already in the game, but have an added stat benefit to make them feel worth grabbing. A few examples of such nodes can be found in the mutator list I’ll write at the end of this post - points 3. and 4.
So I feel like skill tree nodes could be split in two categories:
- Regular skill tree nodes, which provide direct or indirect power to skills - damage, speed, ailments, conversions… Basically every skill tree node in the game right now, save for a few exceptions.
- “Mutator” nodes, which would have a place in skill trees like regular nodes, but would not require any skill point to allocate. They could be shown in another color, with a frame of a color different from regular nodes, or something of the sort.
This way, mutator nodes would still require the player to path toward them, through a path that follows the mechanical identity of the mutator node (for instance, a mutator that would affect lightning-converted Fireball could be positioned somewhere behind the lightning conversion node), but they wouldn’t require any investment beyond that.
This system (or a similar system) would give the devs a lot of freedom to provide varied customization for skills that isn’t directly power-related, which is something that is currently not easy to put in place - as I said before, “mutator”-like nodes that are currently in the game have to provide a stat boost of some sort to be made attractive to the player.
Here are a few ideas of mutator nodes that could be feasible:
- Chaos Bolts and health gain on hit
In Chaos Bolts’s tree, there are two nodes in particular that provide very useful things - Cursed Blood, which can trigger Bone Curse, and Devour the Damned, which can provide mana sustain (which can be very valuable for Chaos Bolts with high cast speeds).
However, those nodes also provide health on hit, which ends up hurting low-life builds, to the point of acting as a roadblock that prevents low-life builds from accessing the other effects of these nodes.
So, there could be a mutator node connected to those two nodes that removes the life gain on hit effect from them.
Note: I wrote a post almost a year ago proposing such a node. However, since I hadn’t thought of the mutator concept back then, I imagined it as a regular skill tree node, which would convert a portion of the life gained on hit into ward. I still think this could be a good way to solve the issue, but I feel like the mutator node would also be a very good way to do it.
- Enchant Weapon and auto casting against bosses
Enchant Weapon has a skill tree node that automatically casts it when hitting an enemy. While this kind of automation node is QoL, I still believe it provides enough benefit to be worth a skill point investment.
However, when playing Spellblade this cycle, I ended up not allocating this node because I wanted to have EW up against rares and bosses - so I used it manually every time I saw a rare or a boss, and only then, which is the kind of behavior that would be nice to automate.
So, I believe there could be a mutator node accessible behind EW’s auto cast node that would restrict the auto-cast node’s effect to rares and bosses (meaning it would only trigger EW when hitting those enemies, instead of the base node’s behavior of triggering EW against any enemy).
Since the player would already have invested skill points into the auto-cast node, I feel like allowing them to choose how their auto-cast behaves would deserve to be made free through a mutator.
- Healing Hands’s “Homeward” node
This mutator idea and the next one are nodes that are as I described earlier: nodes that are already in the game, and that alter the behavior of a skill in a way that can be useful, but doesn’t provide direct power - and since they don’t provide direct power, they also grant a raw stat boost so players don’t feel like they’re a “waste” of skill point.
Healing Hands’s “Homeward” node provides an interesting functionality: if HH would not affect any other player where it is cast, it will be cast on the player themself. This doesn’t really allow auto targeting of enemies - if a player wants to cast HH on enemies in their melee, they can just cast on their character.
As such, if the mutator concept was added, the added healing effectiveness that this node provides could be removed, and the node itself could be made free to allocate by becoming a mutator.
- Heartseeker’s “'Woven Grasp”
The Heartseeker node I’m mentioning changes Heartseeker’s behavior aesthetically - instead of going back and forth through the enemy, the projectile twists and turns around them before piercing them again.
I’ve been playing with Heartseeker these last few days, and the altered behavior looks really cool, to the point that I’d spend a point on it even if it was the only functionality of the node (drip > DPS). But, to prevent the node from feeling “not worth” to allocate, it also gives Heartseeker a chance to slow enemies on it.
Now I put this idea last because I’m not entirely sure it would fit as a mutator. Yes, it technically follows the pattern I described, an aesthetic change with a raw stat boost. But the stat boost feels “connected” to the node - the projectile slows the enemy because, by twisting and turning around them, it maims them by finding weaknesses; unlike the Healing Hands node which just provides healing effectiveness.
So on one hand, I feel like removing the slow chance and leaving the aesthetic change as a free-to-allocate mutator would be nice, but on the other hand, it would make the node lose some of its identity. But I still wanted to mention it as an example of what mutators could provide - aesthetic changes to skills, for vibes only. 
The mutator ideas I provided are only examples; the main idea here is that the mutator system (or a similar one) could be a way to provide a lot of customization for skills that doesn’t fit very well into the current skill tree system - pure QoL features that don’t provide power/automation by themselves, and purely aesthetic changes, being the two examples I showed here.
Thanks to whoever read through my wall of text. ^-^ And if you’re reading this, I hope you have a nice day!!