Agree with your post Mandy ( MrDarcyfan)
I very strongly feel that Neil doesnt know Juhi as much as a serious committed boyfriend whose family is okay with the relationship and they were all ready to go to the next step should have known. There for sure is more to Juhi and RP ka rishta than what was shown.
And neither do I feel Neil was so into thinking of a marriage and child with Juhi - He was committed but at the moment his priority was flying to London and do MBA , not play husband to Juhi or dad to Juhi and Neil ke bacche .
So even if Neil and Juhi were intimate enough to suspect Neil to be father of this girl - it would have been a one off case when they were not really planning it to happen - given Neil was a responsible/committed person though young and ambitious back then.
IF the child actually happens to be Neil's , its not like he has cheated on Avni like you and some others said , however I agree with you that it would be difficult for the general Audience to accept and the show viewership might take a hit . I doubt CVs would take that chance with TRP junta - we online audience and fans of Neil and Avni might accept the Nayi soch ( of Neil being dad yet being with Avni because both of them want to be with each other and love each other ) after lot of bashing of Neil and understand he was not being Ashish Mehta because he hasnt hidden anything intentionally like Ashish did - but the general audience may not accept it.
So its safe for the makers to ensure audience that Neil is NOT the pappa in advance and then follow with all the drama that they plan to do😆 ( just like how they ensured us rightaway when Neil met Juhi again that Neil loves only Avni and not Juhi ) . I really hope they do that .
And RP and Juhi interactions so far also hint the Neil is NOT the dad , its some one else .
Also its very evident like all of you have pointed out ,Neil has never loved Juhi like he loves Avni (I say Not because I am an Avneil shipper but based on what has been shown so far between Neil and Juhi )- so I doubt he would be the dad . It just doesnt go with whatever we have seen of Neil , his character so far and his "Love" for both the ladies.