I just came across this proposal when digging into this topic after reading this thread: Reverse Gas Model need to change
it is great to see that this proposal passed and that this will be tackled in the Thorium Milestone.
having a list of allowed viewers is definitely a great improvement. however, personally I still think that specifically for ICRC token ledgers and other DeFi related canisters, everybody should have the ability to monitor the cycle consumption.
there is always the chance to run into the same issues again as the list of eligible viewers can be changed anytime. another risk is that eligible viewers stop their service and then again, nobody can really monitor this. not saying that this will happen, but it can happen.
if I was building a DeFi app, I would only like to integrate with tokens where cycle consumption can be monitored and where I can proactively inform my users about what might be going on or guide them to top up cycles if needed. and if I identify a specific token ledger which regularly causes issues, I would most likely announce delisting it to avoid further headaches. but even then, if you run a canister for a liquidity pool of a specific token pair, you would somehow need to ensure that liquidity providers get their tokens back before removing it.
I am just throwing out some additional thoughts on that subject.