I'm not sure if y'all recollect, but when vishal went out in BB6, then came back in, he was given feedback by creatives, to work the romance angle with Sana. He mentioned this somewhat loosely, and then kept quiet when further questioned. At that time, LF was totally open, and we could see all that was happening. He went overboard, to the extent of claiming he will date her to Salmaan. By the finals, he was already dating Karishma. Lol.
So, my take in these stories, is creatives are always looking for a love story every season. It gives them TRP, and footage to fill if nothing exciting is happening.
When Sonali reentered as a WC, at that time itself, it looked like it was a plan, and had been the creative teams suggestion for reentry.