I find the manual setup of the synth queue could be improved a lot by simplifying. It's inconvenient to add modules as new recipes unlock and to build the cheapest modules first for fast value. From the queue interface it's not clear for which modules I even have the recipes unlocked, or which level each module is currently at, or how long it would take at current synth speed to upgrade it. The many extra clicks all this takes is not worth the benefits of the precise control I get over the order.
That's why I propose to radically simplify the synth queue: Replace the whole system with 2 checkboxes, on either the synth main tab or the modules tab:
First checkbox says "Use automatic queue". If checked, it always builds the module for which all necessary recipes are unlocked and whose expected remaining time to next level is the lowest of all available (including if the remaining time is zero, i.e. all materials already exist). It updates whenever a module has been leveled, or unlocked, or a newly unlocked recipe allows to upgrade a new module. It may switch the module being worked on even if the currently upgrading module has not finished.
Second checkbox says "Prefer active". If checked, the automatic queue always builds the cheapest active modules first, then inactive ones after there are no more. The auto-upgrade switches the module being worked on as modules activate/deactivate.
If you think the current system has enough value to keep around, you can easily combine the approaches: Keep the "Use [manual] queue" checkbox which would ignore the automatic settings (disable the two automation checkboxes or make the manual/auto queue boxes function like radio buttons) and use the manual setup instead.
Finally, you can make the new buttons an AI upgrade, which would make sense since it's an automation feature.