TL;DR
When a blueprint is placed with a belt, machine or inserter which isn't available, an available alternative should be used, then flagged for upgrade.What ?
When a machine is ghost built, but the machine isn't available in the network at the time, a lower level machine should be built, then flagged for upgrade (though only if it can serve the same role). I'm particularly looking at belts, splitters, assembly machines and modules for this, though it would also help a ton in modded playthroughs.This isn't possible for undergrounds (for obvious reasons - though you're welcome to try), but for standard belts and splitters, its almost certain that something is better than nothing.
This is particularly important with quality, as building a L1 building temporarily until the L5 is available is much better than waiting for the L5 to be available, and stalling a section of factory waiting for it.
In picture form: Instead the drone network should do: The search for an available alternative item should look for lower qualities of the same item, then move onto fast-replaceable buildings which can perform the recipe (starting at the chosen quality level first for each).
The same applies for modules, but moving onto lower versions of the same module rather than fast-replaceable alternatives.
Why ?
Currently a large section of newly placed factory can take a very long time to work due to a small number of missing components - usually Mk3 modules or blue belts, which are both expensive, but have alternatives (Mk1/Mk2 modules, yellow/red belts), which would be better than nothing.This is particularly important with mods adding very expensive buildings, and with the quality changes, it will be really crucial, as copy-pasting L5 buildings might take a really long time to build up, where a factory could be started on L4,L3,L2 or even L1, which would be enough to start off.
This would be really nice for remote bases (or other planets) where materials are arriving slowly, but a functioning base would be important - particularly when that base has to make the materials it needs.