Hey I am working on XISF support in INDI. I have proof of concept done working. To test compile my branch. github.com/nouspiro/indi/tree/feature/xisf_support github.com/nouspiro/indi-3rdparty/tree/feature/xisf_support KStars doesn't support it so you must fire exposure with indi_setprop. After you start KStars with simulator just run these two commands in command line
indi_setprop "CCD Simulator.CCD_TRANSFER_FORMAT.FORMAT_FITS=Off;FORMAT_XISF=On" indi_setprop "CCD Simulator.UPLOAD_MODE.UPLOAD_LOCAL=On;UPLOAD_CLIENT=Off" indi_setprop "CCD Simulator.CCD_EXPOSURE.CCD_EXPOSURE_VALUE=0.5"