You know how when DDO pops out a new Racial variant it does not effect the requirements for racial completionist?
How about a new epic destiny tree for each scion feat that also doesn't count as to having any effect over Epic completionist requirements?
Here's how it would work!
Obtain level 30, select your scion feat, boom the tree for that is unlocked and now appears in the middle of all the epic destiny spheres!
Select your scion sphere and make it active to level it up and use it like you would any other epic destiny tree, except you can only ever have one scion tree unlocked at a time as access to it is granted based on the feat itself.
Scion Of Mechanus Tree for example would have weapon attachment, scaling rust damage on hit, slow-burst guard (Gears of time), Empowered Extend (Extends certain spells like Tensor's Transformation to last a minimum of 15 minutes), and the ability to convert repair spellpower to other spellpowers similarly to how the Tiefling trees allow for such.
But these are just ideas, ideally each tree would have stuff useful for spellcasting, melee, and defensive effects based on the scion feat chosen.