Ah yes the ship based on letter which didn't took even ten minutes of the episode...
Well as most of the fandom I was not exactly keeping track of all the Jonah's simps penpals at first. But then when I started to like Jonah more and I started to be more curious about his past and read some fanfics... You just have to stumble upon this ship sooner or later.
What are your favorite things about the ship?
I really like the tragedy of it. The whole ship is intriguing because it's basically only character about which Jonah shows some sadness over. And fans just decided to go wild with it. Because it's never even implied that they would be that close but... We just like to romanticize regency bastards I suppose.
Also it's interesting to view death of Barnabas as mile stone on Jonah's way of losing his humanity. Since Barnabas was important for Jonah and Jonah could have safe him but he chose knowledge instead...
Is there an unpopular opinion you have on your ship?
I probably don't like when their affection for each other is on the same level. Because yes Jonah liked Barnabas but I would like to imagine that he was more of enjoying being adored and loved and never fully reciprocating the feelings.