Is it a core requirement of how LN functions that any time state of the channel can be included in the Bitcoin blockchain or is it just because LN is not yet fully developed. Hopefully a clever solution can be found to fix this flaw.
Older LN channel state is cryptographically valid the same way as newer state. The only incentive not to trying to add older LN channel state to Bitcoin blockchain is the other party with newer state can punish it by getting all such channel coins for themselves - but only if the tansaction can be added to Bitcoin blockchain in timelly manner (you can set the time how long your fine to have stuck your LN coins when opening the channel - this corresponds to the time available to react for having confirmed tansaction in Bitcoin blockchain should this scenario happen). This has theoretical attack vector possible with big LN hubs and congested Bitcoin - like with exchange hacks, it is only matter of time when such attack become reality one day.