Should motorbikes and cars share lanes? How to deal with left turns (the dangerous ones) in junctions? Should motorbikes and bikes have to do two-step left turn?
There's an idea that we should categorize vehicles as human-poweres or not. Is this a good idea? How about paddle-assist-only ebikes?
When there's not enough space for lanes, which type of vehicle get compromised?
I'm a fan of the 3-tier system:
In the best case there is space for at least 1 lane of each. If not, then some compromise must be made. Pedestrians should never be completely removed, so the conflict is between groups 2. and 3.
What to do should depend on the purpose of the road. Roads meant for long-distance travel prioritize cars, there is no real help there. Although I'd argue there should be a combined pedestrian+bike path alongside even inter-city roads.
On city streets see if there are any parallel corridors that go roughly in the same direction. Then you can divide the traffic onto different streets. One street for 1+3, and the other for 1+2. Or course this only works if you have nearby parallel streets.
The final option is combined low-speed zones where everyone shares the same space. It works great for neighborhood access, it's very inconvenient if you want to go a longer distance in car.
But if you're in a situation where the road is so tight you can't even put 2 proper lanes on it, that road should probably not be used as a thoroughfare.