I would be glad to concede your to your position if you can prove that John had the entire completed cannon of scripture in mind when he wrote that. I believe your position takes his words out of context. In Rev 1:3 it clearly indicates the context as meaning the words in Revelation and gives no room for anything else. There is no doubt that all of scripture is inspired by God, but the entire cannon of scripture as we know it today was not in view anywhere in Revelation.
John did not write the book of Revelation, per se; the Holy Spirit did. Thus it is the Holy Spirit that guided John to write 1:3 admonishing us to read and take heed to the things written in the book, and the same Holy Spirit that tells us:
For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book: (Revelation 22:18)
John was the youngest of the disciples, and the one to have outlived them all. This was his last book, and thus put at the end of the canon of the NT, and appropriately so.
John knew that he was writing under the inspiration of the Holy Spirit, as he was told to write these things down by God himself. The apostles knew which epistles were inspired and which were not.
And account that the longsuffering of our Lord is salvation; even as
our beloved brother Paul also according to the wisdom given unto him hath written unto you; As
also in all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest,
as they do also the other scriptures, unto their own destruction. (2 Peter 3:15-16)
--Peter refers to Paul's epistles as Scripture. Even though Paul had written more than just the 13 epistles contained in our canon he also wrote to the Laodiceans, and two more epistles to the Corinthians. But both Paul and Peter knew which ones were inspired.
This second epistle, beloved, I now write unto you; in both which I stir up your pure minds by way of remembrance: That ye may
be mindful of the words which were spoken before by the holy prophets, and of the commandment of us the apostles of the Lord and Saviour: (2 Peter 3:1-2)
--If you study verse two carefully here you notice that the Bible is divided into two parts: the OT written by the prophets, and the NT written by the apostles. Peter tells them to keep in remembrance the words of Christ and the apostles (that is the NT), and puts them on the same level as the inspired OT.
To say that the canon is still open today is a ridiculous position to take.
First, according to the Bible, every prophecy would have to be verified, and everyone that had uttered a false prophecy would have to be taken out and stoned. Would you do the honors?
Second you have an editorial problem. From the first century until now and all over the globe, if the gifts are still in operation, then all those words of knowledge, those prophecies, those messages in tongues (languages) are all inspired. Whether they are from believers in Africa, Asia or here they all have to be gathered up, collated, and put into great tomes (for there are many), because all would now be a part of the canon. All the "I have a word from the Lord), the vision from God, the dream from the Lord, the word of knowledge, what God spoke to me, etc. They all have to be collected and made available for all. Otherwise how will we know what God's complete Word is? We can't. Will you be the "chief-editor-in-charge"?
Third, you have no answer for the total lack of evidence of any of the sign gifts taking place today. If the canon was not closed, revelation would be accompanied by signs and wonders. But those have ceased. There are no tongues, no miracles, no prophecy; none of these gifts that can be exercised in a Biblical way today.
