Keep Ranks Earned
Reduce required points for ranking
Keep current design on rank
Maybe it should work something like the Tempered buff. At the end of each Iron Banner, you get a medallion based off of your rank. Come next IB, you can use it to buy a buff that increases your Rep gain rate (except for the duration of the whole event, unlike Tempered). The amount it buffs is based off of how far you got in last IB; higher rank means greater buff.