Thank you too for your comprehensive opinion and for enjoying game :D
About slot machine, your proposal is a very interesting idea, however I was not able to implement it better. What I can to add (according to my previous answers) is that power-ups or its symbols planned to be collected at lanes and be activated. So, current implementation is about 20-25% of the very first idea.
Controls are the next (I think less but still) disadvantage, but I also mentioned earlier about my decision. Changing lanes can be very hard, even impossible when too much red boxes will be spawned (however I implemented a “backdoor” too not generate three impassible boxes in the same wave).