[css-flexbox][css-grid] Abspos static position / placeholders

Everybody's least-favorite topic! (Mine anyway.)

The section on static positions of flex items is marked at-risk.
It's an open issue in Grid Layout. I'd like to start a discussion
on this topic, with consideration for
   - what makes sense for Grid Layout
   - what's implemented so far for Flexbox and Grid
   - aligning Flexbox and Grid, what about these two specs should
     change/stay the same to make their behavior consistent?

Flexbox:
   http://www.w3.org/TR/css3-flexbox/#abspos-items
   # The static position is intended to more-or-less match the
   # position of an anonymous 0×0 in-flow ‘flex-start’-aligned
   # flex item that participates in flex layout, the primary
   # difference being that [extra packing space is not introduced].

Grid:
   http://www.w3.org/TR/css3-grid-layout/#abspos-items
   http://dev.w3.org/csswg/css-grid/#abspos-items
   # An absolutely-positioned child element of a grid container
   # does not participate directly in grid layout. Its static
   # position is ???
   # a) The before/start corner of the grid container? (In this case,
   #    should we adjust Flexbox to match?)
   # b) The before/start edge of the cell it would be placed in,
   #    if it were a 1x1 auto-placed grid item? (Don't let it
   #    generate new rows/columns, though, which complicates
   #    things.) (This is closer to Flexbox's current behavior.)
   # c) The static position is affected by the alignment properties,
   #    as if it was a 0x0 thing floating around in the containing
   #    block. (Defaults to the start/start corner, since ‘stretch’
   #    can't do anything to it.)
   # d) Other?

Thoughts? Suggestions? Data? Proposals? Use cases?

~fantasai