I think the changes to AS 1.16 would make reintroducing chain mining feel much better than before with little change to existing systems. my idea would be a perk, likely near top left (evorsio), that converts the player's mining size usage from an AOE to a chain mining effect. The player's mining size would increase the size of the chain, making this method compatible with the infused crystal pick, Evorsio mantle and existing perks without needing many new perks for it to scale.

I'm imagining the issues of chain mining in the past were:

1. the player not having much control of when to chain mine when they did not want to
2. difficulty having a cost/limiter for the ability (as it used to be chance/cooldown I think)

In 1.16+, the first issue is no longer thanks to the ability toggle, and the second issue is no longer due to the expansion of the starlight charge system (chain mining would consume starlight charge like the AOE does).

now that I think about it, the term mining size leaves it a lot more open for different mining variations. (maybe this was intended and something similar to this idea was already thought of. ¯\ _(ツ) _/¯ )

There could also be a perk that converts the player's mining size from a 2 dimensional square AOE into a 3 dimensional cube. the cube would have a smaller surface area but an added depth.

Both of these perks should scale in a way that they are less useful at lower mining sizes but become more useful as the player's mining size increases. so at mining size 1-2 having that 3x3 - 5x5 is still the best choice, but if you want to make the chains or cubes really powerful, you have to invest in mining size points. This also gives incentive to have builds with high mining sizes, because although I love watching my 17x17 at near max mining size, right now having a really high mining size is kinda just a flex.