How about, as a function in conjunction with Epic Reincarnation, we get a new tree that we can populate, similarly to twists (i.e. drag & drop), with our own custom ED tree. Say one tier per EPL up to 5. 4 slots on tiers 1 & 2, 3 slots on tiers 3 & 4 and 2 slots on tier 5. You populate them with abilities from your locked EDs. Make the auto-granted abilities linked to available per sphere, as well as possible tiered powers. Have the tiered powers be unlockable to other spheres that differ from the base ED sphere autogranted abilities through some sort of earned mechanism similar to how fate points allow you to unlock twists, have some other earned point based on number of completed tiers in destinies during your current incarnation (the unlocks per tier to do not persist through ED TR and you have to start anew with the obvious advantages from your number of locked EDs from doing epic past lives).
For example, say you have 3x EPLs, locking 3 EDs (Primal, Shiradi, Fury). You can populate your custom ED with up to tier 3 powers from any of those three locked EDs, and the autogranted abilities can be selected from only those available in the Primal sphere. You grind on and cap all of the Martial sphere's EDs during this life. This allows you to incorporate any power from any Martial sphere ED up to tier 3 into the custom tree, but you still maintain the Primal autogranted progression only. Then you epic TR again, lock Legendary Dreadnought, unlocking tier 4 in the custom tree but clearing all settings in the custom tree from your previous life. This time around you still can only use the Primal sphere as your base progression because you only have that sphere completely unlocked (3 locked destinies in a single sphere are necessary to even begin a custom tree). As you lock more EDs through epic reincarnation, you gain alternate base progression possibilities (so, say you eventually lock all EDs in the Martial sphere, you now can select from the base progression abilities in Primal and Martial). Eventually, if you Epic Reincarnate enough, you will be able to create your own tree entirely from any abilities available in all EDs.
In the meantime you also push out a crapload more epic content and end game purpose, otherwise there's no point to all of this grinding except as busy work.