There is no "focusing" on code. The only thing that you can provide for programmers to generate more code is more time to do it. So you are either "focusing" on code for new or current product or older product.
If you are running "lean" with just enough programmers to "finish" the product as physical demand for shipment of product deadlines approach and pass for the company to remain solvent, resources like time become no longer available as the transition to the next product has already begun.
We should remember a place in time not so long ago when Stern games shipped with much fuller, all but finished code with rules, dots and sounds for all features at the time of shipment.
More programmers would likely initially be a hindrance as they curved the learn of the platform and basics of pinball code and how to implement it so the designer's expectations were met.
Like it or not, a "finished" pinball machine is one that accepts money, provides a certain amount of play/entertainment, and then ends the game so more entertainment can be purchased again. Anything beyond that is "unnecessary" added-value for the consumer.
The consumer can only affect the production model by choosing not to purchase the entertainment at the offered price point. Complaining after the purchase is too late. You are at the mercy of production schedules and available man-hours for any added-value content. A manufacturer running lean may never revisit that product for added-value content (wheel of torture).
More programmers is a long-term solution. More time during production is a short-term solution.
Entirely un-informed and uneducated opinion on my part, but that's how it breaks down to me.