Sorry missed this when it was first posted, this is a great post thank you! Was admittedly slightly afraid when I saw the title 
. A few responses below:
Finally note that the rollup blockchain doesn’t inherit the technical security of the parent chain. In other words, posting the data (and proofs) from some blockchain to Ethereum will not increase that blockchain’s security. The usage of Ethereum’s data availability is solely for the benefit of the rollup bridge, not of the rollup blockchain. That implies then that the rollup bridge includes the smart contract and the data availability on Ethereum, and that the rollup blockchain is, well, just a blockchain.
Could you elaborate here? I don’t think I would agree with this if I’m understanding your argument correctly. As described in the post, a “sovereign” rollup (i.e., no bridge) can still inherit the technical security of its base layer, so it’s not only for the benefit of the bridge. Also as described in this great thread by @sreeramkannan.
But sovereign rollups, by definition, do have a full node bridge from the base chain, since full nodes of a dependent blockchain need to be full nodes of the base chain.
I don’t believe this is true? You either need to embed a base layer full node within the rollup full node or have the ability to run a trust-minimized light client (eg, with DAS). If you were to launch a sovereign rollup on Ethereum today, you would then need to embed an Ethereum full node in the rollup full node. However, that’s due to current base layer implementation, not fundamental to sovereign rollups (and can change in the future for Ethereum).
Most rollups have some “escape hatch” mechanism planned, which really is just an automated fork mechanism. In our example, if the Near blockchain fails, the bridge could change into a based rollup , allowing anyone to update the state of the bridge, as long as it comes accompanied by a validity proof
This is a very interesting area! Actually reminds me quite a bit of what Anatoly had tweeted about recently as described here. Also an idea for a “trust-minimized” bridge between two chains without being a “rollup” necessarily, where the bridge could again fork away. Still need to think more about this/potential issues.
Sometimes I don’t agree with your conclusions (for example, on shared sequencers)
Just curious what you disagree on, always fun to chat on 
This is a great post and really enjoyed reading it, thanks again for the thoughtful response!