The Disassembler is a block used to basically de-craft stuff. It would have two grids once you click on it. You put the object(s) you want to de-craft in the first grid, and the ingredients will appear in the second grid. There would be a 12% Chance to get extra ingredients once you de-craft. You could find it in dungeons or craft it with 1 Crafting Table, and 3 Iron Ingots.
Why the chance of extra ingredients? It seems like this sets up a resource generation loop: craft an item with expensive ingredients, de-craft, repeat. You could do it all standing in place. This doens't seem like the sort of thing that should generate resources.
As to de-crafting in general, I'm not sure. Ideas like this have been floated, and featured in mods, for many years--it would be convenient. But I take it that part of survival play is that if your choices matter because your resources are limited--and that if you use a resource for something you may not be able to use it for something else is part of that.
The metal in many items can be somewhat reclaimed now, though at significant loss. There's also repairing. And that seems to reflect where survival is at with regard to reclaiming resources. Full de-crafting would entirely change those dynamics.
As T0gaJohn has noted, the chance of 'decrafting' returning 'extra' ingredients (presumed to be more of one or more components than originally required to craft the item rather than just 'random stuff') seems an invitation to abuse (consider applying this to something like a beacon).
Without that feature the idea may be viable, but…
Some idea of what the intended use would be would be helpful:
allowing dyed/colored wool to be crafted back into white (eg bleached) would not be likely to be seen as overpowered…
a similar argument can be made for glass, beds etc (there are also fairly popular mods that simply allow one color to be directly dyed into another so at least some positive interest in such a change seems assured)
crafting doors (or the like) back into ingots would raise the issue of handling recipes that produce multiple items as output. This example (6 ingots > 3 doors) would be simple as the division is even allowing a return of 2 ingots per door, but not all recipes have that feature (stairs as example.)
another issue would be how far back the disassembly would go ie would disassembling a 8 ladders yield 56 sticks, 28 planks, or seven logs?
further, if something like sticks is disassembled, what type of planks/logs would result?
There is also the strain on credulity of some disassembly operations: turning glass bottles back into glass blocks seems quite reasonable, but disassembling a cake into its ingredients does not (even with magic and MC physics).
One thing that seems certain with hte size and diverse intersets of the MC player community: if a 'thing' is exploitable, that exploitation will be found and used.
Means of handling (or limitations that avoid) the sorts of questions above is needed before anyone attempts to implement a proposal (be it into vanilla or 'just' a mod).
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WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.
IMHO all metal objects should be able to be smelted back into metal nuggets with almost-1:1 return, but non-metal objects are the way they are forever. (Except wooden items, which can be used as furnace fuel.)