Bzzt. Wrong. Speaking only for myself, I say it must be possible. But does that mean sinless? That's not what it says. It says we will not fulfill the lusts of the flesh. It doesn't say we'll never have an impure thought. In fact, it doesn't even say we won't HAVE lusts.
Even if it went that far, does that mean we can claim we actually walked in the Spirit so perfectly that we were sinless? How can you claim such a thing? How do you know you're walking in the Spirit so perfectly that even the least little self-deceiving error tainted your thoughts for a moment?
Don't you see the arrogance in that claim? It's self-righteousness once removed and a contradiction in terms. "I'm not sinless but I'm so good at walking in the Spirit that I am sinless."