In Robert Slowley's comprehensive comparison of the 1984 NIV to the 2011 NIV (as well as the TNIV) he states that in the 1984 edition the use of the word for occurred 7,219 times. In the 2011 edition it occurs 7,273 times. So the 2011 version increased the count by 54.
Regarding Romans 1:18 the CEB, EHV, NABRE, NCV, NLT along with the NIV, do not have the cherished word for. And you know what? It doesn't change the meaning of the verse one whit without it.
Concerning Isaiah 12:3 the same goes. The meaning of the passage is not hindered a bit with the precious word therefore. The following translations (among others) do not have that unnecessary word :
CSB, CEB, ESV, ISV, LEB, NABRE, NCV, NET, NLT, NRSV all joining with the NIV.
Over the years I have shown you that the singular they has been in use for more than 500 years. The usage began in your nation. It's not an Americanism alone. I have given you a sample of your own usage of the singular they, along with examples from James White and John MacArthur. It's just a fact of life in conversation. And it shows up in periodicals, newspapers and books.
I have also admitted to you that there are cases in the NIV in which it is awkward at times. Until ta or thon (I prefer the latter) can take its place the singular they is here to stay.