I have a few suggestions, at least one I know has been suggested already.
First is add a backpack slot, backpacks (double chest inventory), ender-backpacks (easy and convenient access to ender-storage) and switch elytra to use backpack slot (ability to use elytra and still have chest armor).
Second is a higher tier or two equipment.
Third is a series of decorative light blocks
Fourth (the one I really want) sun beam blocks that project light like sunlight, preferably vertical and horizontal, but I would settle for vertical. This would be useful for tall rooms such as the ones you would need for underground tree farms, or to light up a shaft.
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