Imagine that your build queue has a pointer at it's right most edge. This pointer has always been there, but you've never noticed it until now. This pointer is the reason that all build orders are added to the end of the queue. What about adding a toggle switch to "Unlock Queue pointer" (Or some better name) Now you can drag and drop the pointer up and down the length of the queue pointing it at the gap between any 2 build items or the start or end of the queue. Now, without damaging your existing queue, you can start inserting items into the queue. You can decide to temporarily interrupt your stream of low level tanks to create a couple of extra engineers. Having created these, your factory would go move on to those items which had already been in the queue, but which had been bumped by the engineers. Just another thought. What do you think?
Whilst the ideas are very similar, they are not the same. I posted them separately because often 1 idea is overshadowed by another when they are both mentioned in the same thread. Mention X And Y in the same thread, and someone will decry both because they don't like X.