Densely targeting emission line dominated objects with NIRSPEC MSA

Notes on an obvious/crazy idea that has fermented in various people's brains,
and recently re-emerged from conversations involving Marijn Franx,
Daniel Eisenstein & HWR; these thoughts were floated at the
May 2016 NIRCAM-NIRSPEC meeting, with basically positive reception to the group there.


Conjecture: for emission-line dominated objects it is possible/sensible to open
many more shutters than the conservative "no overlapping spectra" targeting might suggest.
[For the time being, this pertains to NIRSPEC R=1.000 or higher resolution.]

Starting facts/assumption:
-- the spectra of most faint, high-z (z>~5-6) galaxies are emission line dominated.
-- the potentially most interesting ("PopIII") galaxies are emission line dominated
-- the # of targets that have potentially detectable emission lines in 10^(4-5) sec NIRSPEC
   exposures is far larger than the slit real estate budget, assuming no-spectral-overlap.
   [galaxies with broad-band magnitudes ~30 may well have strong, hence detectable lines...]
-- for emission line dominated spectra of (very) faint object, only a tiny portion of the spectral
   range therefore contains "significant" pixel.

Consequences:
-- the vast majority of detector pixels contains no "interesting" signal
-- many faint high-z emission line galaxy candidates will go un-targetted in
   any one deep NIRSPEC MSA setting.

Proposed remedy (to be taken as a though experiment, first):
open ALL shutters at focal plain locations that plausibly (according to NIRCAM photometry)
have high-z, presumably strong emission line targets.
[spectral overlap and chip gaps be damned for now.]
Let's take N~5 as a mental strwaman-plan.

[Nomenclature: dispersion runs along 'columns', slit runs along 'rows']
Let's presume that means we would have N shutters open in any one column (on N galaxies).
Advantages: N times more targets
Disadvantages:
  a)  N x higher sky background
  b)  "confusion of N overlapping spectra"

Addressing the disadvantages:
 on  a) How does the monochromatic surface brightness of emission lines (say, 10Msun/yr at z~6)
  compare to the background? I.e. are the cores of strong emission lines above/below the background.
  NB 1: compared to 'slitless' spectroscopy the background
  is still N/365 lower than slitless. [365 == # of shutters in dispersion direction]
  NB 2: the ensemble of open slits will inform us about the background

 on b) lines are narrow and sparse; if the continuum is negligible; the spectral signatures
 don't overlap. In principle there is some wavelength degeneracy
 (which line came through which slit); but this should be manageable, as long as there are
 no shutters open in the same column and adjacent/nearby rows.
on b): information on the continuum will be severely degraded;
 --> for emission-line dominated objects, there is little information in the continuum anyway;
 photometry will help

One specific approach is to target all objects that were done on R=100 mode, in R=1000, with disregard to overlap problems. The R=100 mode should break many of the degeneracy issues.
[Thanks to Chris W. for suggesting this.]

Basis of this: could one get Brant's and Christina's mock -data catalog, including their photo-z estimates?