Slimes are certainly a nifty little block, able to push and pull just about anything. The only problem is that they push and pull just about anything. Meaning that you have to surround them with either air, obsidian, or block entities, which can sometimes make it difficult to incorporate them in an aesthetically pleasing manor. It also means you can't put them directly besides one another in a redstone mechanism without them interacting. With these facts in mind, I came up with a possible solution:
Boxed Slime (please excuse the quick-and-dirty render. It's mainly just for illustrative purposes)
My idea is to introduce a new block with the same sticky/bouncy properties of slime on one of the six sides, with the other five sides behaving as a normal block. The direction which the slime-side faced would, like pistons, be based on your camera angle. While the crafting recipe could consist of one slime block surrounded by eight seven wood planks (any type):
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I'm confused by the slime block, sticky piston, and what you suggested: slime box.
If the slime box was implemented, wouldn't it function similar/the same as a sticky piston?
But if my "theory" is proven wrong, I would love to give you full support.
(Correct me if I am wrong).
No, it would function like a slime block... extending the push/pull of pistons, as well as thrusting entities... but only in one direction. This way you wouldn't have to surround it with air/immovable blocks as you do with regular slime blocks.
1. Allow the block to change direction depending on the way it is placed, like furnaces and pistons (though you probably already have this in mind)
2. Allow this to be made with a selection of blocks depending on the block used in the recipe (for example, boxed slime in stone bricks instead of wooden planks)
3. Change the crafting recipe from:
(W is wood, S is slime block, O is empty)
This is just nitpicking now, but the current recipe seems to suggest that the wood extends a little beyond the slimeblock. Obviously, this change would mean that that block can also be crafted by shifting all items in the recipe up one tile.
Full support whether you make these changes or not, though