While playing through, I noticed another block I was carrying around repeatedly was the crafting table. I thought it'd be handy if I could instead open a 3 by 3 crafting grid on command without having to grab a block.

I would recommend restricting this to the vanilla blocks for game balance such as the crafting table, maybe the anvil for repair in the field.

I couldn't find any other add on mods that added this functionality and I thought this would make a great companion at the same level as the light focus or the water focus since they effectively replace the need for stacks of torches or keeping a water bucket.

[EDIT]

I wanted to offer thoughts on implementation, though of course final implementation decisions would be at the mod owner's discretion.

In keeping with the user experience for other foci, I was thinking the selector is the block to mimic on cast,
ie seperate foci for one set to crafting table, versus one set to anvil, versus one set to vanilla ender chest.
similar to how one would need two foci if they wanted to break with silktouch vs break without.

limit range choices to either touch or self, the difference being click anywhere to load the ui, vs click the side of any block without an existing right click event to instead perform the event from the cloned block.
It wouldn't make much sense to use plan, projectile, bolt, etc as one wants the interfaces locally.
Maybe on touch if used on another player could allow sharing utility without having to pass a gauntlet or focus around, but not sure how hard that'd be to implement or if that'd lead to griefing.

shards required could be distilled from the primary aspect of each block maybe if attempting to set programmatically?

My suggestion would be to make this compatible with more focus mediums. With plan, touch or bolt it would spawn a temporary "ghost" version of the chosen block. For examble, you could summon a ghost crafting bench that you could interract with. The time could be modified, with longer lasting ghost block increasing the cost and complexity.

A fun interaction would be anvils... Falling anvil spells, anyone? :)

My suggestion would be to make this compatible with more focus mediums. With plan, touch or bolt it would spawn a temporary "ghost" version of the chosen block. For examble, you could summon a ghost crafting bench that you could interract with. The time could be modified, with longer lasting ghost block increasing the cost and complexity.

A fun interaction would be anvils... Falling anvil spells, anyone? :)

Setting a block as a falling anvil would easily be accomplished by the swap focus, no?
either way I think that would be out of scope for a utility focus I imagine.

Another implementation that might be possible:
make it so shift + right click on a block to map it to the focus, right click to cast.
ie taking a template of the vanilla crafting table would bring up the 3 by 3 crafting grid at will.