Possible science goals for reionization:
The physics of the epoch of reionization is very poorly constrained at present. kSZ, together with other probes can provide important measurements that can potentially distinguish between different scenarios. kSZ can measure the duration of reionization and physically motivated goals include:
A) If the reionization sources are galaxies (fiducial model), we would like to distinguish between the following three scenarios: 1) part of reionization is produced by Population III stars in minihalos M < 10^8 M_sun and T_vir < 10^4 K. This could create a long tail of reionization (say x_e ~ 10 - 20%) out to high redshift (z ~20 or higher). 2) Reionization only by high mass atomic cooling halos (HMACHs) with M>10^9 M_sun. 3) Reionization by high and low mass ACHs (including halos with M < 10^9 M_sun).
B) Be able to detect a tail x_e > 0.1 at z > 10 if present. If it exists, it would significantly bias our measurement of tau from the low L CMB polarization power spectrum.
Ancillary (or harder/more ambitious):
C) Measure the tau clustering from reionization and determine the mass of halos containing the galaxies driving reionization.
D) Place constraints on non-standard models such as reionization driven by quasars, X-ray binaries, Dark Matter annihilation etc.
E) Combine measurement with 21cm observations (for example through cross-correlation) to improve redshift resolution.
F) Measure physical reionization parameters such as the mean free path of ionizing photons, efficiency, escape fraction etc.