I think that scaling only weekly rewards would be a mistake. All three trials, DSA, Vet DSA and weekly rewards should scale up. Reward the top players for their achievements but don't completely lock out everyone else from even having a shot at items at v16. Only scaling weekly rewards would still be obsoleting the content for over 95% of players that would probably never be on the leaderboard.

If scaling the content is seen as too much of an undertaking, then perhaps add a rare drop widget to the end chests that allows you to boost the level of an appropriate trial/dsa item by +1 when used. That way ZOS doesn't have to spend man hours scaling content and players get their potential end game gear. Top leaderboard players could get multiple widgets in their mail for upgrade purposes