All of my thoughts are very practical, so I'm not completely certain which way is the best to introduce the least overhead for Steem/the developers.

Whether we have separate inflation pools or one inflation pool with separate individual staking rewards (2 months = you get 5% of the pie, 6 months = you get 10% of the pie), as long as the end result is that stakeholders will have the ability to decide on how long they want to stake their Steem for, in return for benefits (increased APR, witnes & sps voting rights - maybe even with a multiplier, etc.).

This will result in a far more stable outcome, which can even be marketed in a really good way: Invest in Steem on your own terms, as if we'd go the quick and dirty road of changing the power-down absolutely.