So automation is a fairly ubiquitous concept in many mods. However, the industrial nature of them is completely incompatible with the survivalist ethos of vanilla minecraft. Still, I believe this can be implemented in a balanced way.
When mining, perhaps one may come across an underground cave. In that cave, perhaps one might find a corridor with rooms, clearly built by something. Inside are diminutive cave people that are hostile to outsiders. But if you manage to kill them and clear them out, you’ll find chests with their belongings, and some strange devices! Perhaps they’re a remnant of some past civilization - The stronghold builders? The lost miners? Whoever built them must’ve been advanced!
These machines might do anything from cutting down trees to mining to planting crops. They could save you plenty of time and labour! However, they’re old and rusted; they won’t work as well as they might have and they might break down easily.
They would require a silk touch pickaxe to mine and take home. When a redstone signal is applied, they would be activated. They cannot be turned off, and will continue to operate until they break. They would move completely autonomously, outside of your control. For example, a lumber machine would cut down as many trees as it can within a certain radius. However, you better hope your wooden house isn’t in the way!
These are the advantages I see in this feature:
-Another interesting feature for the underground
-A novel endgame tool
And here are possible disadvantages
-These could be used for griefing
-These may be underpowered if used at a high tier
Let me know what you think and how I can perhaps improve the concept!