If i had to guess, i would expect the new gear to be more of a transition then reset. It has to be better then what we have now but not so over the top that the current gear we have serves no purpose.

IE: new heavensward Lvl 50 dungeon gear would have an ilvl of about 120-125, have another AF set at about lvl55/ilvl130 and then at lvl60 have a 'tower' like set for 140 and a 'coil/tomestone' set for ilvl150.

This way we could have a few more options for while we level, and then it just blends in with the current ilvl increases.

I would doubt they would reset the ilvls, as it would require a lot of work for no gain. (all the DF is set to the values already) Since all the other 'new gear sets' bump up by 20, i would expect it to be the same, just stretched out to make the leveling worth it.