Does one know a time frame when this will be fixed or a work around?
Actually the Survey123 website now already supports IWA authentication since 3.2 release on Jan 31, 2019. You can see the reference to this in the What's New here: https://docdev.arcgis.com/en/survey123/reference/whatsnewsurvey123.htm
Unfortunately, the known limitation on the following page (which I assume is where you got the bullet point from above) in the doc was not updated in time, so will be updated for our 3.4 release and this limitation removed:
Retrieving data ...