1. Theres already been requests for spliter/merger hybrid
2. Yes, please, this would compact factories further
3. Im not a fan of it, when you have #2 you can have multi-output buildings therefore handle >180 output using only mk1 belts if you are creative, it would not be possible if S/M are capped, my only concern is that, without a speed cap and #2 people would start making lines of splitters to exploit its speed
4. So, lets say at input to #7 smart storage you have a #2 connected #4 overflow splitter that would redirect any unwanted items to either #5 trash or storage.
5. An item destroyer will be useful, i end up with items in my inventory i don't need.
6. i'd rather have a restrictive system that encourages creativity than a confusing one with unnecessary components
7&8. Other than a truck station, you should have different containers for different items,an order system is a bit of an overkill
Over all i like #2 and #5, but congratulations on a neat ecosystem.