Many others have already predicted that Akash might be the actual kidnapper. It sounds really twisted at first. Why on earth will Akash kidnap the one person he looks up to?
Shyam being the kidnapper is way too obvious. Maybe today's confrontation with Khushi was just to divert our attention. But what if he really isn't the kidnapper?
There actually quite a few reasons why Shyam can't be the kidnapper.
1. He already has the papers.
2. When Khushi asked him to come to the airport, Shyam had already found the papers and he was waiting for Arnav to get on the flight. If he has the papers and Arnav leaves for, why would he kidnap him? Arnav doesn't know he signed the will. Khushi doesn't know Shyam swapped the papers after she read them. What's the point of kidnapping?
Why I think Akash might be the kidnapper.
1. His changing attitude. During the Bubbly track, we saw the glimpse of a different Akash. Someone who get's irritated quickly, jumps to conclusions and acts brash - a trait we never saw in Akash before.
2. After ASR left, it was mentioned on several occasions that Akash is working way too much. Even more than Arnav. That's something he hasn't done before. Why would Akash suddenly become a workaholic? Which project is he working on? And why would it be mentioned so many times?
3. The kidnappers haven't hurt him and they were specifically instructed to give him his meds on time.
If Shyam is indeed the kidnapper, he being so concerned about Arnav's health is a bit odd. He is not calm and focused and may not think so hard about these things. Besides, Shyam is less likely to know so much about Arnav's medicines.
4. There was too much focus on the motive behind the kidnapping. Khushi suspected whether Arnav has any enemies. Shyam isn't Arnav's enemy in the typical sense.
Most importantly,why is mami helping Khushi? What's the significance behind it? We always knew mami is good hearted and loves her niece and nephew. She sold her jewelries for Arnav in the past and she just adores Anjali. Mami could have warmed upto Khushi in some other situation. Why now?
Will mami have to choose between her blood and the nephew she loves like her own at some point?
Akash is someone viewers won't suspect. So he being the kidnapper will be a shocker for the audience. IPKKND has only one villain. Bringing another villain will thicken the plot. If Shyam is not the kidnapper, his track can be continued for much longer.
Is history repeating itself? We know Arnav's chacha betrayed his brother, took all their properties and threw Arnav-Anjali out of Sheesh Mahal after their parents' death.
Why in NK coming? We know NK is good guy who doesn't harbor any ill feelings for anybody. He was never jealous of Arnav, is a good friend of Khushi and he is righteous. He caught mami when she spiked Buaji's drink during sangeet. Is he going to be the actual Lakshman of the story?
EDIT...I don't want to see Akash as a negative character. But something has changed about Akash, Even if it's not the kidnapping, we will surely see some other twist involving Akash soon.