I would be very surprised if the final system is significantly different in structure and major content from what we've seen so far.
They'd come across as looking rather ridiculous after talking up the merits of each adjustment they've made if they went and tossed it all out and gave us something altogether different.
Will there be differences? Of course. The math will get revised, how often certain classes get stat bumps/feats, what the exact benefits of each feat is, when a given class gets a given feature, the exact price of various items (who knows, maybe they'll go back and revisit their earlier idea of a silver standard?), etc.
But I'll go out on a limb and say we'll still get stat bumps that can be sacrificed for feats. We'll still get backgrounds that grant skills. We'll still see attribute-saves rather than 3E Fort/Ref/Will saves, 4E Fort/Ref/Will defences, or old-school "Save vs. _____" categories. The modified-Vancian spellcasting for wizards will remain largely unchanged, with some fine-tuning. Clerics will still be the healers. There'll still be a lack of inspiration/shouty healing in the standard rules (though an included-at-launch module might appear). Combat will still be designed for fast pace and without the assumption of a grid and minis. Ranges and speeds will still be measured in feet, not squares, metres, inches, or other units. Barbarians will probably still be called Barbarians, no matter how often people point out that that's a background, not a class.
I'm quite curious as to what sort of changes the people who think we'll get a "quite different" system are expecting to see. Perhaps we're just defining "quite different" differently.