TL;DR
Making trains able to wait for the condition of all storage slots (40 per cargo wagon) not being empty.What?
Train wait condition, like 'Full Cargo', except it specifically checks all storage slots of all wagons for not being empty instead of all them filled strictly with full item stacks. This is in order to deal with mixed insertion problems... which is now a natural phenomenon if you do 'quality' production directly on into trains.Why?
Quality drilling (-> quality smelting) -> train wagon (belt insertion/direct insertion, no storage insertion).That train will deadlock. You probably already get what situation I'm talking about....
Example situation
I ran into this problem of parked trains deadlocking in train stations because their wait condition "Full cargo" never gets reached.It turned out the inserters were deadlocked because they couldn't insert the item on the belt of a certain quality level since all stacks inside the wagon of this quality were filled, and only a different quality level of the item had an incomplete stack in the wagon. (I hope u get what i mean)
Intuitive solution, no hacks:
Trains should just be able to count filled storage slots, of any level.That plus an inactivity wait condition would solve the situation adequately.
Better to have this than doing big spaghetti belts into trains, storage chest setups on every station, circuit magic or somehow modding Quality itself.