Points you invest in your pre-upgraded weapon will not be wasted. Someone who goes into 7.2 with a 54 weapon traits will, after upgrading, be a few traits ahead of someone who goes into 7.2 with only 35 traits.
However, new ranks of AK will steadily devalue current AP in playtime equivalent, while the increasing costs of traits will devalue current AP in purchasing power. For the time you spend acquiring AP now, you'll get sixteen times as much when you reach AK 40 a few months after 7.2 launches.
So the consequences of vendoring all of your AP tokens now would be:
* Right now you won't get the small power bonuses (which do add up, even if they aren't a lot per rank).
* When 7.2 launches you'll likely be 1-3 traits behind what you would have if you had acquired the AP.
* Eventually the difference will fade to less than one trait.
* You'd have some extra gold, though perhaps not a lot of it.