Other changes one might imagine are include the sorts of variable demand-sensitive block rewards as described in Vitalik's post. With fixed block rewards Bitcoin is inherently subject to enormous price volatility in the presence of any demand volatility, and that may over time turn out to be non-viable.
It is foolish and short sighted not to realize that bitcoin is an experiment in progress, and may have gotten one or more fundamental things seriously wrong.
Before you assume I'm trashing bitcoin here and respond accordingly, note the emphasized use of "may" in both of the above paragraphs. Serious risk factors exist.
Also note that bitcoin is priced for at most a 0.1% chance to succeed in a big way on the scale of fiat. If you think the probability is actually 1% then you should bet big on bitcoin, but it can simultaneously be rational to bet on alternatives that might succeed on that scale instead of bitcoin.
We may be in agreement here. I would argue that there is a chance block rewards will need to be reworked, though not in a way that will affect current holders much, or at least not for a very long time.
A better way of making the point I want to make is that the bar for scrapping the entire ledger is extraordinarily high. If reworking the coin issuance schedule is necessary, it makes sense to do just that rather than have a completely different competing ledger.
Turning to an argument based on magnitudes, if we assume the "backup ledger" is worth 10% what Bitcoin is, the Bitcoin ledger would have to be something like 90% screwed up before it would make sense to change over. Coin issuance changes wouldn't be that level of change, at least not for maybe several hundred years(?).