Shillelagh is a solid Tier 1 cantrip option for druids. It provides magical bludgeoning damage and allows the druid to apply their wisdom modifier to melee attacks. However, shillelagh lacks the standard damage scaling that other cantrips have, so its usefulness drops off significantly even at 5th level, and by 11th level when other damage cantrips are dealing 3dX damage, shillelagh starts to feel like a wasted cantrip selection.
To fix this, I want to add the standard cantrip damage scaling to shillelagh (addendum in italics):
The wood of a club or quarterstaff you are holding is imbued with nature's power. For the duration, you can use your spellcasting ability instead of Strength for the attack and damage rolls of melee attacks using that weapon, and the weapon's damage die becomes a d8. The weapon also becomes magical, if it isn't already. The spell ends if you cast it again or if you let go of the weapon.
The weapon's damage increases by 1d8 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8).
This would bring its damage into line with the other druid cantrips (produce flame, poison spray, thorn whip). Now, as I was thinking through this change, one glaring issue came to mind: the Magic Initiate feat and the Extra Attack feature. Magic Initiate would allow non-druids to learn and use shillelagh:
Choose a class: bard, cleric, druid, sorcerer, warlock, or wizard. You learn two cantrips of your choice from that class's spell list.
For a fighter, this would make the change to shillelagh potentially problematic, as the fighter gets to make three attacks per Attack action at 11th level, and this would set their base damage per attack to 3d8+STR. This seems obviously broken, so I'm pretty sure this is why shillelagh does not feature the typical cantrip scaling.
However, in an upcoming game, I am planning to play a single-classed druid. Single-classed druids don't have an Extra Attack feature, so the only balance concern I could come up with is off the table. It does synergize similarly with haste, as haste allows one additional weapon attack per turn, but the only druid that can learn haste is Circle of the Land (Grassland), and I am playing Circle of the Land (Coast), so unless another party member has haste and chooses to use it on me, haste will not be affording me additional attacks.
The game I’ll be playing is starting at 10th level, so my goal here is to see shillelagh be viable in late Tier 2 and into Tier 3 play without being overpowered.
Have I missed anything else? Is there any other reason just adding the standard cantrip damage scaling to shillelagh for my single classed druid might be unbalanced?