Add 1 tile or a constant combinator near every input/output. So we can place a constant combinator or something else and mark what the ingredient or product goes over pipe/belt there (for blueprints)

EDIT: This is simply to indicate to the player which item it should connect in these pipes/belt.

This would cause a lot of clutter. For me, adding this feature would cause me to obsess over setting the correct signals for every input. It should be simple to add standard combinator ghosts to the blueprints.

For blueprints and markings what shall be in those belts/pipes peoples usualy use constant combinator nearby. For Factorissimo you place these constant markers outside of factory in the corner or above input. So you know what shall you bring in.

I dont see a reason marking interior of factory what shall come in or out. But of course you can still use constant combinator nearby and mark it this way.