Reading Blockstream's introduction article on Eltoo and one paragraph says:
[..] in eltoo all participants share a common set of transactions, unlike LN-penalty, which requires asymmetry in which participant has access to which transactions, in order to tailor the reaction to the misbehaving party. This change eliminates what we call toxic information in Lightning. Toxic information comes from transactions belonging to outdated states, which if leaked will result in the loss of funds. This happens not only if a party misbehaves, but also if a node forgets about an update (e.g., when being restored from a backup). With eltoo this is no longer possible because only agreed-upon states can be settled (i.e., eltoo is penalty-less).
What this seems to imply to me is that it's not possible to broadcast an old channel state and have it accepted by the network, and this would seem to greatly simplify some design issues we're dealing with today. I strongly feel like I'm misunderstanding something here and would love to get clarification from someone more knowledgeable. Thanks