So this is a very common suggestion I've seen ever since the ability tree came out and I never understood why it never happened, Poisoned Blade and Double Slice always confused me as neither of them really represents their archetype well and neither have an impact on their archetypes by the end game (double slice can on melee builds but again acrobat isn't even remotely a melee class) most abilities have a decent impact for what they are end game, but are still fairly balanced early game.
Shadestepper is a burst damage class and poison is the exact opposite of that dealing damage over time, but even if poison did make sense the max you can get is 50 which is extremely low, acrobat on the other hand has double slice which makes even less sense since if youre playing the class correctly you really shouldnt ever be in melee range let alone using your melee unless you're using a mana steal build which idk why you'd do that, but either way I think these two classes could use some abilities that are balanced in the early game, but scale into the endgame well.
I would propose giving Shadestepper precise strikes as it emphasizes burst damage and scales off of one of the two main elements that shadestepper represents, it never made any sense to me that warrior got precise strikes over assassin and while archer having it makes more sense I'd still argue that it makes less sense than assassin having it, assassins are precision killers and shadestepper represents that incredibly well, preceise strikes would definitely be a welcome addition to a bit of a weaker archetype.
For acrobat it's a bit more simple, I would propose an ability similar to wisdom being an ability that grants mana regen based on your walkspeed or vice versa as I would argue those are the two most important stats for the archetype especially with propellor hat being added (idk when but it was added after I quit a year ago) and it does a much better job representing the archetype than double slice.