Nuclear argument is an extreme example. If you disconnect a city from the net for 24 hours the chain will be forked enough to make it unusable (by current propaganda). This is not acceptable if the aims are to be "the currency" of the world. If 10 minute transaction delay is bad, imagine 24 hours or a week.

But the block repackaging problem can be fixed without much pain and without voiding bitcoin warranty (i.e. no double spend, all still valid etc). There's so much mining power now, we can repackage anything in no time.

If the incentives are right we can have transactions approved within milliseconds because the network is very strong and can can be in a constant state of (useful) hashing and making blocks. Right now a lot of resources are wasted searching for random numbers by increasing the complexity of the hash.

The 51% computing power balance ratio will still hold true. You need to make lots of reasonably secure blocks all the time by a diverse group of packaging agents.