Does anyone have experience using psyllium husk in place of gelatin. (My particular situation is making marshmallows)
Do not use psyllium husk. It tastes terrible and no amount of sugar will mask the taste.
Try using agar-agar instead, that's what vegans use for vegan marshmallows.
In Asia, they sometimes use konjac for it, but you will have to be very careful eating it because people die from accidental choking.
I do not have much experience of using it but perhaps I read in some place that Agar or Corn starch is used as a substitute of gelatine.