What's the year 4 risk? He isn't going to officially retire.
I don't think it's a huge risk but let's play it out:
ARI or BUF (or other team near the floor) add Weber to easily reach the floor while actually paying salaries well below the floor.
3 years later that team is better, has some players on new deals that require raises, plus they sign a UFA or 2. Now they are at or near the ceiling. While they can then put Weber on LTIR (teams trading for him won't be doing that until they are close to the cap)... that may mean that they run into overages, lost bonus cushion and other factors that might limit their cap the year after Weber's contract is done.
Personally I think that's a long shot to happen as I don't see ARI being up against the ceiling in 4 years, but theoretically it's possible.