I suggest that the NIV translators wished to head off questions related to "Eternal Security". And the KJV doesn't deal with the question. My perspective is that 2 Peter 3:17 says nothing about "Eternal Security" one way or the other. It is not pro or con. The topic is not in scope. So, it's wrong headed to build a doctrinal position on this verse. But, (I think, obviously) that needs some explanation. I certainly don't wish to invalidate the OP's question. Tthe short version is the text points to who Christ is.
2 Peter 3:17 is the closing part of an Inclusio, the beginning of which is 2 Peter 1:12
Here they are side-by-side (NASB20):
Therefore, I will always be ready to remind you of these things, even though you already know them and have been established in the truth which is present with you.
You therefore, beloved, knowing this beforehand, be on your guard so that you are not carried away by the error of unscrupulous people and lose your own firm commitment, 18 but grow in the grace and knowledge of our Lord and Savior Jesus Christ.
Notice the two bolded phrases which serve as antonyms of each other. And those phrases point to something that is firmly established.
I've included verse 18 in the second citation because it points back to 2 Peter 1:2-8:
Grace and peace be multiplied to you in the knowledge of God and of Jesus our Lord,
...
For if these qualities are yours and are increasing, they do not make you useless nor unproductive in the true knowledge of our Lord Jesus Christ.
So, this letter sized Inclusio brackets a lengthy monologue about the dangers of false prophetic information about what it means to be "the lord Jesus Christ". The letter points readers to the "knowledge of Christ."
So, Peter is closing out the topic of the entire letter. That topic relates to what it means to "know the Lord Jesus Christ." And, most importantly, this knowledge of the Lord Jesus Christ is comprised of behavior that is productive for the Christ. One can't escape the emphasis on action expressed in 2 Peter 1:5-7, and especially considering the word 'unproductive' in verse 8. In other words, knowledge of the Lord Jesus Christ is not something you circle on a multiple choice test. It somehow involves action. The words Peter uses are γνῶσις or ἐπίγνωσις.
This point is important because it means that "knowledge of Christ Jesus" is more than just "believe in him". It's about adopting his identity as the one who molds who I am.
Recent neuropsychological research suggests two types of knowledge (actually 4): Conceptual Knowledge and Procedural Knowledge. Conceptual Knowledge aligns quite well with what the Greeks termed "οἶδα" (to know). γνῶσις (to know) and its cousin ἐπίγνωσις (to relate to and so know) aligns quite well with the meaning of Procedural Knowledge. The former is knowing which answer to give on a test. The later is accurately and consistently completing another person's sentences. You know that person. This type of knowledge is the knowledge Peter is instructing his readers to grow in.
And the body of the letter is a very stern warning about getting the prophetic word from the wrong people. Why? Because having my identity molded by false prophecy is dangerous. When that happens, we loose the foundation of the truth.
This paints a context within which one needs to interpret 2 Peter 3:17. In other words, there is the "prophetic word made more sure" (2 Pet. 1:19) that speaks of the Christ, the one seen by Peter (and others) [2 Peter 1:16-18], spoken about by the Prophets [2 Peter 1:19-21], and taught by Paul [2 Peter 3:15-16]. And, testified to by God himself (2 Peter 1:17). This is the 'steadfastness' referred to and declared to be our very own.
With this, I disagree with Calvin1. He places 2 Peter 3:17 into a purely hortatory genre, and I don't think you can separate encouragement from a basis in fact. That's not to say that this verse isn't hortatory, it is. But, I think it's wrong to split the encouragement of the text from a doctrinal position of the text just because one assumes the text suggests a doctrinal position (which you disagree with). I don't think it suggests that doctrinal position (so, you can't use the verse in support, either). It posits that the Christ, and the truth of the Christ--who he is and what he has done--as that which is rock-solid. The entire epistle of Peter points people to focus on the revelation of Christ Jesus--that's the point of the letter!
What does 2 Peter mean? It means, Focus on the revelation of Christ Jesus; He is the one with whom, in whom, we have rock-solid, full assurance; don't believe anyone that says anything contrary to that.
What this means practically speaking is this: If you believe that your faith secures your salvation, then you aren't believing in the rock-solid foundation to begin with. You might have faith, but it's not in the right object. Stepping away from the wrong object does not mean you've lost the right object. It means you've lost the wrong object, substituting a new wrong object. Unless, of course, you substitute the right object, which is Christ Jesus, the rock-solid foundation.
Finally, our commitment is to a person who
...knows how to rescue the godly from a trial, and to keep the unrighteous under punishment for the day of judgment (2 Peter 2:9).
Which brings not only a sobering sense of seriousness to the topic, but a place of profound rest. He knows (οἶδα). He'll get the right answer on this test.
And a sidebar: I don't think any translation needs adjusted. It's more that the phrase, ἵνα μὴ τῇ τῶν ἀθέσμων πλάνῃ συναπαχθέντες ἐκπέσητε τοῦ ἰδίου στηριγμοῦ, however it's translated, refers to being carried away from a "secure commitment to practiced truth". It's not referring to being carried away from a "secure position of salvation." 2 Peter is written to believers to encourage them to tenaciously hold to solid doctrine centered on Christ Jesus.
But, thankfully, that underscores the fact that our salvation isn't tied to a perfectly held doctrinal position, either. Nor even tied to the practice of truth. If so, then 2 Peter is written purely to unbelievers to scare them into believing, and the whole Eternal Security question goes out the window anyway. c'est la vie.
1"It seems that the assurance of our salvation stands on slippery ground and hangs suspended as if on a thread, since he warns the faithful to beware that they do not fall from their stedfastness(sic).
What, then, will happen to us if we are exposed to the danger of falling? I reply that his exhortation and others like it are not made with the purpose of undermining the security of our faith which rests on God, but of correcting the idleness of our flesh." -- Calvin's New Testament Commentaries, Hebrews and I and II Peter, page 368