The workaround against both options is to simply split the stake to different accounts. Both make it more difficult to overtake the chain with a minority stake but it's better than the alternative.
The current setup allows for a 51% attack instead of the theoretical 2/3 +1 that is needed today...that is very clear.
Limiting the number of blockproducers that a stakeholder can determine has other tradeoffs so it's a complex problem.
No, it's not. See A splitting stake to A1 and A2 in my article. He can maximize usage of his stake, but still unable to take all the seats.
If you can point out these tradeoffs. I can't see any. 1 SP = 1 vote simply allows for better decentralisation. JS made an educated decision about 20 candidates, but the average person would not :)
I can imagine a situation where 2 or 3 different versions of the code are running side by side that create different forks that do not agree on the last irreversible block. Each version being supported by different cartels with no clear way of breaking the tie.