Btw , do u happen to know why they cut the handkerchief scene? It was even cut in the international version so I'm not sure if its just because of Korean ratings. But its crucial enough for all the actors to repeatedly confirm it and share it. Do u have any idea why?
Director & co. cut the scene because they thought it was best. We never get the exact reason, but there were apparently several discussions about it amongst themselves. Disregarding the set-up in every aspect (writing, ost, etc) for Soo to reunite with So.
But I can tell you with 100% certainty that the scene was not cut because of domestic ratings. First off, it was the last episode so whatever they did literally would not affect the drama going forward. When ratings affect dramas negatively, the dramas usually get less episodes, but this couldn't happen here because SHR was pre-produced. (And I don't think the ratings were so abysmal to warrant that anyway.) In other cases, if a production is able to pin-point why audiences are unhappy, they'll re-edit. Which did in fact happen in SHR's case, but this happened in the beginning and lasted until nearly the end (but there were less and less major changes as we reached the last couple episodes). The re-editing was done in fact to favor both Wang So and the development of SoSoo.
The only actors I know that have gone on record about this are IU, Lee Joon Gi and Ji Soo. I can't remember exactly, but I believe Ji Soo was actually the first to say anything. He mentions it in an interview, but later that part of the interview is taken out. Very ~suspicious. As for IU and Joon Gi, they would obviously care about this the most since it concerns their characters. But their reasoning, in the end, is pretty simple. Fans wanted to see a happy ending and were pretty distraught, and they sought to comfort us. JG talked about there being more during his mini-fanmeeting, while days later, IU would post the handkerchief on her IG.
The two would continue to make plans as JG ended up changing the date for his Taiwan fanmeeting to coincide with IU’s concert. This would allow for him to guest at her concert, and for her to do the same at his fanmeeting. They would then go on to re-create the rain scene, and then the cut ending.
Frankly, IU and JG went so far as a treat to the drama's fans. They wanted to let us know that So and Soo do in fact reunite. From the actors' comments, you can tell they thought this cut scene would be released in some way, but the production hates us that never came to be.