Tomes in patch 2.4Follow

If they stick to their pattern with how they handled Philosophy Tomes, they will retire Myth, allow you to convert them to Soldiery, remove the weekly Soldiery cap and introduce a new type of Tomestone which will be capped weekly. Also, the former Myth items will either become drops in dungeons, or purchased through other means (I believe several Myth items can be bought with Allied Seals even now, so this may be the permanent replacement).

But, there's no guarantee this is what they have planned at all. We probably won't hear about the plan for a couple of months yet.

I don't think Tome cycling was originally intended. It may not be necessary to make changes to tomes this go around.

The retire old currency and bring in new currency was something that WoW did starting back in the first or second expansion. It became necessary because players would stockpile the old currency and on day one of the patch, you'd see them walking around with 2-3 pieces of the new gear. It also had the bonus effect of allowing newer players to pick up gear just a step off of current raid gear, which assisted Guilds (FCs) gearing up new players to replace people that quit/retire.