My proposal for a new feature is adding the confession dial from Season 9 and make it so when you right click with the confession dial in hand would teleport you to the inside of the confession dial and once you find the exit and go through the portal  you would be sent to gallifrey

also you could add the Veil from Heaven Sent as a boss in the Confession Dial dimension

the world gen for the Confession Dial dimension would be the clockwork castle build TheTwelfthDoctor is making

support!

also, maybe adding certain blocks, such as the clockwork cogs or whatever, and the x400 stronger than diamond (can't remember it's name) block, which would take a long time to mine but it maintains it's damage for roleplay

Support and just for suspense add the monster which forces the confessions. That way at the end you have a choice of the last confession or breaking the wall and trying and trying again until you break it, you'd need to lower the time it'd take by A LOT otherwise 4.5 billion years, either MC years/days of punching it would be WAY too long for it to be fun.

 But the bird used it's beak and the doctor used his hand. So a pickaxe wouldnt take so long

I think the wall should be about 6 blocks thick, since the wall in Heaven Sent was 20 feet long, and that's about 6 meters.

Sounds good.

And I think the blocks should just be 0.5x harder than obsidian, so a player without efficiency pickaxe has to mine a looong time

It should be that Obsidian without efficiency on Iron is the break speed for Efficiency 5 diamond 

What if you've got your bare fist like in the episode? Then that might go under what I said as taking too long and killing the fun.

It could be that stone, wood and fists take gold time, and regular gold efficiency 5 is gold efficiency 1.

Sounds good.