You are right about the GUI, but regarding quests being too easy, consider that anything in your statistics page can be a quest: Kill some withers, mine a bunch of endstone, etc.

There are some ideas on the reddit rejected and fps lists that I would like to see…

Automatic crafting, block placing, block breaking, villager trading.

Doors, trapdoors, bars, and chains in gold and copper. More orientations for bars and chains and glass panes.

Vertical slabs and stairs. Concrete slabs and stairs.

A lamp whose brightness equals it’s Redstone signal strength and a sensor whose Redstone signal strength equals the block light level.

Both recipes use the same amount of Amethyst Shards and the same amount Glass.

The recipe using Amethyst and Stained Glass uses half as much dye as the other.

The recipe using Tinted Glass and Dye would be present for players who upgrade their world and had previously crafted lots of Tinted Glass.