You know that Luke wasn't in existence yet when Paul wrote this to Timothy. Paul wasn't referencing future writings that, centuries later, would be compiled into the tome we now call "Scripture." He was referring to the OT. Go back a few verses and you will see this clearly:
14 But as for you, continue in what you have learned and have become convinced of, because you know those from whom you learned it, 15 and how from infancy you have known the Holy Scriptures, which are able to make you wise for salvation through faith in Christ Jesus. 16 All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness,
See it? Paul is talking about Holy Scriptures that Timothy has known since infancy. What are those? The OT.
Is the NT inspired as well? I think so. Does 2 Tim. 3:16-17 say so? Absolutely not!
Why don't you see the 'point', Paul actually refers to 'all scripture'.
Apparently, there is for now written down, cum there is to come and written down later.
All that will be eventually 'inspired' or 'breathed out' by GOD alone, whether now or later.
Then which was with the Jews like Timothy and are disciple likewise in.
Where similarly, at first Moses orally spoke, and then later 'inspired' or 'breathed out' by GOD to have them written down.
As well the Gospel at present for the Jews, which apparently is not written yet at the moment.
Since similarly, are orally proclaimed and made disciple of all nation at first.
Until later they were 'inspired' and 'breathed out' by GOD to be written down.
And reliable books were selected and compiled together, moved by the Holy Ghost.
Where in my time, Jesus' work through His 'instrument' Paul's same words 'all scripture' still 'resonates'.
As actually similarly referring to what GOD finish 'inspiring' or 'breathing out' and have left us with finally.
The 'HOLY BIBLE' without a doubt.
And conclude, do not 'limit' the HOLY ONE of Israel and HIS Word.
Which will not go 'void', but accomplishes what it is sent to do.
Still don't get the point?