I love your 4th and 5th idea, OfUnknown. Mostly because it works so well in LoL and other games like that where it is very competitive.
If ranks were to be reset yearly, that would be great. It means that if you want to keep a high rank, you need to actually play the game instead of just attaining rank 1 and then quitting the game.
Perhaps if this was implemented there could be a large-scale event each year where players from different leagues/tiers compete against each other for a prize of some sort (eg. tier 1 players vs tier 1 players: big prize because it has bigger competition / is hard to win. tier 5 v tier 5: small prize because not as competitive /easier to win than tier 1 comp).

Some further ideas for this:
1) To rank up between each tier you need to do a series of ranked matches and if you fail to win then you have to wait a certain period before having the chance of ranking up again.

2) If you're inactive after a while and fail to complete ranked matches within a certain amount of time then you are demoted to a lower tier / if your rank drops too low you get demoted.

I feel this could work if ranked servers were put in place with a limit on how many ranked matches you can do per day.