This sounds like a good plan except that is it not true that the direction of development now is on layer 2 rather than on chain? I think the size is still a problem so they would like to restrict it on chain like that and keep those 100k transactions all on Lightning.
There is simply no way that transactions are done entirely on lightning or on layer 2. That is unrealistic and makes Bitcoin completely useless and which is why I've criticized repeatedly on the fallacy of having a limited on-chain capacity and banking on off-chain TXes to sustain the TX volume. We absolutely need a capacity increase in the future to even think of mass adoption. Again, 7TPS is ridiculously small and lightning network isn't (and should not) be the solution to the problem.
Again, the problem we're looking at right here is not to ensure that we maintain the same level of security. The whole point of PoW is to make it more expensive to attack the chain than be honest. If there is a substantial security decrease but we're still looking at a huge discrepancy between the profits from an attack vs profits from mining, then there is no problem.