Yes, -니 뭐니 is like "etc." or "and what not" as you say. You can say things like 아빠가 네 선물이니 뭐니 잔뜩 사 왔다, 집이 부자니 뭐니 (하며) 자랑한다, etc. There are also other unrelated constructs that have the -니 뭐니 form. * X-니 뭐니? = "(is it) X or what?" e.g. 너 바보니 뭐니? = Are you stupid or what? * 뭐니 뭐니 해도 = you might think this or that, but ... => when all's said and done / what matters in the end is ... e.g. 뭐니 뭐니 해도 우선 건강하고 봐야 한다 = No matter what, you should have good health first.