What a fascinating question. There's a long answer & a short answer. I might find the time to write up the long answer one day.
I'm more interested to know what you think is missing? And who you think has the authority today to add to Scripture? Could your question be inspired by this verse from the Gospel according to John?:
But there are also many other things that Jesus did; if every one of them were written down, I suppose that the world itself could not contain the books that would be written.
Personally, I'm glad I don't hafta carry the world around with me every time I go to church, or find the room for it in my humble abode.
But the short answer is that Refreshed is quite right. There are severe strictures and warnings, both explicit and implicit, against adding to the Word of God. Those attempts that have already been made to add to the divine revelation have not ended happily.
You want some examples? The pseudepigrapha are so-called for good reason - they are writings with false titles. They claim apostolic authority in order to give them the gravitas, credibility, and authority they need to fool Christians into accepting them as inspired writings. But they were written some 50-100 years after the last Apostle died. They are therefore a plain fraud at best, or a demonic attempt at 'another gospel' at worst (see Gal. 1:6-9 and 2 Cor. 11:3-4).
Mohammed added the Quran (aka Koran), and founded a new religion. A long succession of popes added 'tradition' and idolatry, and succeeded in emasculating the doctrines of grace for a major branch of the faith. Charles Taze Russell, Edward Irving, Joseph Smith, Ellen G White, Madam Blavatsky, Herbert W Armstrong, David Berg, David Koresh, Jim Jones, et al and ad nauseum, added their own 'revelations', and...... well, you must know by now how that story ended. The fact that none of them agreed with each other should alone tell you something, nevermind the rest.
So no, unfortunately the long and sordid history of attempts to add to God's word is a study in self-deception and human folly. It should also be a salutory warning to anyone who thinks they have what it takes to assume such a role for themselves.
Now listen to me...I have a message for you that came directly from God. Ignore it at your peril. Now give me all (or at least some of) your money to support this great work of God. He will surely bless you if you do, and give you back x10 what you gave me.
Catch my drift?
I know what you're thinking. If that was the short answer...........!!