Here is the full rules texts that I've written:
https://scribe.pf2.tools/v/8oZobzJ0-implement-rules

Edit: I changed the rules now to include all spell attack rolls, not only cantrips. Original post still below.

Hello Reddit,
I have thought of a (imho) simple and elegant solution for the obvious imbalance across all the currently existing offensive cantrips.
I've been reading and having discussions about Electric Arc and its inferior brethren since the release of the CRB and now finally set out to try and make a small adjustment in the right direction.

Background: in PF2E, spell attack rolls are notoriously harder than weapon attack rolls as they cannot be improved through items, yet still attack the same AC (as compared to touch AC in PF1E). In addition, casters gain proficiency slower than martial characters do with their weapons, making enemies of equal or higher level rather hard to hit with something that costs 2 actions and doesn't do anything on a miss. On a comparative note, the Electric Arc cantrip can target two enemies and still deals half damage on a "miss" (aka a successful save from the respective foes) and oftentimes their Reflex save is worse than their AC, making it even more of go-to choice.

In order not to imbalance everything else, I limited the implement status to only cantrips, although there might be a case that it could be applied to all spell attack rolls. However, I will leave that to you to decide.

Please let me know what you think, I would greatly appreciate any feedback received if only for grammar or spelling corrections (non-native EN speaker) or formatting improvements.

TL;DR: Implements are homebrew handheld items/weapons that grant weapon potency rune benefits to cantrips that make spell attack rolls without unbalancing everything else. All magical staves are also implements and there's an optional weapon property rune that can be attached to any weapon.