Reddit user beybladeparm has pointed out an interesting piece of trivia. Every single NXT singles champion (both men and women) that has been called up to the main roster is now on the WWE Raw brand.
NXT Champions
Seth Rollins
Big E
Bo Dallas
Neville
Sami Zayn
Kevin Owens
Finn Bálor
Samoa Joe
NXT Women’s Champions
Paige
Charlotte Flair
Sasha Banks
Bayley
The Tag Team Championship situation is actually pretty much the opposite, with most former champions who were called up now wrestling on the SmackDown brand.
NXT Tag Team Champions
Neville and Oliver Grey (Raw)
The Wyatt Family (Erick Rowan and Luke Harper)
Neville and Corey Graves (Raw)
The Ascension
The Lucha Dragons
The Vaudevillains
American Alpha