I think, the dress somehow was an indication if one were to see - of the time that Khanak can let go of the burden of her past , the one she carried - a bit more than she could bear ( be it the financial suppport for her Ada and Bai or being a suraj for them) - The sari perhaps was an indication of her grownup self taking on new responsibilities, but with Shaan getting her the new outfit, I saw it as him reminding her that it was fine to all young and not be so grown up... that salwar was that indication...the salwar was an indication of the freedom that Shaan showed her...helped her experience, all the while being in touch with all around her, the past the present...
What does one really want ultimately, being with the person you love, the freedom, you always experienced ..but this time, the pleasure of being able to enjoy that with the one you love... and yet be yourself!
Most of the times, we do not need to put everything in words or explicitly, but subtle gestures say it all.
If anyone, Shaan saw her for what she was, right from the day they met thru all that she had to face, and he was there too. He just knows what she is like and what makes her happy... its that connect that was established that is the reason for this comfort they have with each other!
Am so sorry for rambling, but that scene had quite an impact on me and I couldnt stop thinking...
Thank you bearing with my rambling!