This is the general idea about the mechanism behind HPPD, yes. But wouldnt it be simple just try an antagonist in, let say, five people? We would know instantly if this is the way. It should have a profound effect on HPPD if the theory that everything starts with 5-HTP2A and is the cause of most of the symptoms.
As dr A said, the most probably way to find a cure is for people on this board trying new meds, backed by different theories about the cause of HPPD to give some credit in what to try.
So, i believe the progress in search of a cure or symptom relief is up to ourselves. Thats why it so important to post about what we try and why in the pharm section. Imo, we need more Guinea pigs. There is too much talk and to little trials.