Wow that's an old thread you're referencing. This thread covered content that was in development during the DotN beta, so the contents of the book trumps what was discussed there.
I can shed some light as to why shade powers cannot be maintained: the game system wants to make sure accounting is minimal, meaning any maintained effects have physical representations (ie runes in play) to remind everyone about an ongoing power/effect. The issue with Shade powers is the binary effect, so if maintained, then the question is which effect is ongoing? First round easy to remember, but a few Sceadugengan powers maintained for a few rounds and ...pandemonium!
