The Android example you provide shows 'spatial inconsistency' relative to the device edges, but spatial consistency relative to the content: the 'clear all notifications' icon is always in the same place relative to the list of notifications.
The choice the UX designers made here was not between 'icon always in the same place' and 'icon always in a different place' but rather between 'icon always in the same place on the screen' and 'icon attached to the content it affects'. This is a common pattern on variable-sized content: Instagram photos and the like/commments link, Gmail emails and the reply box.
In this context, your list of benefits/drawbacks of 'spatial inconsistency' is, I think, a misnomer.
The benefit to the design that was chosen, IMHO, is that a user has likely just finished scanning their notifications — from top to bottom — when they want to clear all. So their eye and their attention are already at the bottom of the list. Further, if the notification list is long enough to go off the screen, in order to 'clear all' the user has to scroll through the list. This has the benefit of making sure that they in fact do see all their notifications before they clear them.
You need to take the larger context of an OS redesign into account, as well, when asking why a specific design decision was made. The choice to reposition the 'clear all' button was in the context of a larger overhaul of the Android notification system. From what I can tell (I'm not an Android user, but I have done a fair bit of research on this for this question), Lollipop now maintains a consistent status bar at the top of the device. Previously, viewing notifications would replace the status bar with a context-specific bar that had context-specific buttons. The new design doesn't allow that, so a new approach was needed.
All that said, you can definitely make a case that they should have placed the button at the top of the list (below the status bar), and I think we could come up with some pro/cons for that vs. the design they chose. But it's a different question than the one you've posed here.