If anyone is interested I made a build that can make most items at the highest quality possible using a single assembler by switching the active recipe on the assembler. You just throw in the basic resources for the base items in the recipe and it just builds the whole thing at legendary quality.

https://www.reddit.com/r/FactorioBlueprints/comments/1gl5v50...

It takes a bit of setup for each item you want to make though and doesn't work if the process takes more than one fluid. The default in the blueprint is to make blue circuits.

Unfortunately factorio has this mechanic where if you switch the item an assembler is making it loses progress for productivity bonuses, so this setup is not really practical for many items. Plus it takes a lot of space. But it is fascinating to see it work.