Anyway, can you say at least one real argument against removing RS under checkpoints ?
It isn't possible to independently verify the chain. This significantly elevates the trust model for checkpoints from choosing among valid chains to trusting that the chain below the checkpoint was valid before being trimmed. Again, tradeoffs....
The chain is verified by the fact that the block hashes are immutable. An attacker can't change the transaction data by even 1 bit and get congruence with the block hash history.
It is only a risk against an attacker that has 50% of the network hashrate and thus can rewrite the chain, but in that case you have bigger problems any way.
Thus afaics, TT's concern is BS.
Everyone seems to assume that the difficulty is constant when it is actually an amazingly fast exponential. You don't need >50% of the hash rate to rewrite past blocks. On the contrary, most of the weight of a particular chain is in the newest blocks.
Those ring proofs are still available (somebody is saving them) if we need to reconstruct from a discovered bug. In the meantime, no need to force everyone to download them every time we sync, which is a significant problem for XMR as I've read some users complain.
And if you think about how to radically decentralize mining as I have been doing for months, then you will realize a long download time for syncing is a significant issue.
(I repeat, "the jury is still out...")
If everyone is not storing, then those who store will have an information advantage.
In XMR's present case, full nodes store everything.
In XMR's future case, full nodes store everything and SPV-style nodes store just a cache of what they need.
In BBR's present case, "somebody" stores everything and full nodes do not store rings.
In BBR's future case, "somebody" stores everything, full nodes do not store rings and SPV-style nodes are still required.
Do you see where I'm going with this?