Indeed, BIP 106 is an extremely interesting proposition. I discovered it thanks to your post OP, thank you for sharing.
I'm surprised that it hasn't attracted more interest in 2015 and the little feedback we can find about the realism of its actual application.
In order for Bitcoin to succeed, blocks must be full.
If blocks are never full, then there is never a reason for a transaction to pay more 1 satoshi in fees. As the subsidy is reduced, fees become more important. So at some point, full blocks will be necessary in order to ensure that the revenue is high enough to discourage a 51% attack.
Changes that attempt to prevent full blocks would directly impact the security of Bitcoin.
This is a very valid point, from a long-term perspective. It's true that once the block reward will be low, if the fees were low, we could see a decrease of the global network's hashrate - even if a 51% attack is difficult to consider today (because of 358.2 EH/s and the biggest pool -Foundry- "only" own 35% of the hashrate) doesn't means that it won't be possible in the middle/long term.
So yeah, as I understand, with BIP 106 you remove the mempool's congestion problems, but replace them with a potential problem linked to fees that are too low, and therefore to a mining income that is potentially too low to ensure the network's security. Are there any other points that would make this proposal negative for the network?