Expiration wasn't a paid option at all - it was like currency, and in fact a currency that didn't depreciate no less because they didn't count what you paid, they counted what you bought (how many days and parks). Expiration as a paid option was a later addition they offered, presumably as a compromise that also netted them up front cash.
(you are only thinking about the MDE transition...)
Countdown.. the point is it constrains the discount to that stay... limiting the use of the discount (and its intented purpose and motivation). It proves Disney isn't just trying to give you cheaper tickets... even tho some see 'my 6 and 7th days are cheaper.. just what I wanted!' - because they focus on the outcome, not how they got there.
Combine - back to the currency discussion.. tickets can no longer be treated as units you can combine. If you take three old 2 day park hoppers.. they will only issue three seperate tickets now. Where this comes into play is imagine you have a pile of 1 day park tickets. You think 'wow, worth $100 each!' and you go and say I want to have a 5 day trip paid with those 1 day park tickets. A 5 day ticket is cheap, I will combine these tickets.. no. Instead what you would get is 5 1day tickets, meaning you would have traded in the full $500 value to get what equates to a much cheaper ticket (5 day ticket).
Bundling is referring to things like length of stay options, coupling party sizes to dining/package options, etc. This one is more in the finer details that aren't universal to all cases.