Sorry, why that? More work for sure but what makes it tricky?
It's a lot more work that's for sure, likely more work than it would be worth.
There's the difficulty of getting everything just right where there's enough space for stuff to fall down but also have the knob protrude. A secondary profile would need to be routed into the backside of the lid so that the knob would fit far up enough. This would involve making a routing template and doing a tedious setup to align everything perfectly.
I don't have a spherical lathing attachment which will make the production of the knob take quite a while and require each to be hand fitted to the lid
There's also the matter of attaching the knob to the lid solidly without obscuring the opening of the container too much. The thicker the supports for the knob the more likely that material will get stuck on it rather than falling down.
Lastly I would have to spend time dimensioning, lathing and producing all the pieces of wood required for the additional feature.
The amount of effort to add it and do the job properly would drive the cost up quite a bit. It would add a lot of complexity for very little functionality. I've been using my prototype bin for a week or two now and I've had no issue with tapping out my vapourizers on the edge of the hole.