Johnsteinbeck's seeding note is an important observation. Even if we assume that Fed loses tomorrow's finals at Wimbledon, the prospects are very high. It is very easy to calculate how much will be the addition as per Wimbledon's grass formula.
They add 100% of grass points won in the previous 12 months. That includes the 1200 points (earned at Wimby 2015) + whatever he will earn in Halle in 2016.
They add 75% of the best points obtained at a single event in the 12 months prior to the above period. As Roger made the finals of 2014 Wimbledon and got 1200 points there, this number is 900 (75% of 1200). This is fixed and it won't change.
So, the Wimbledon formula will add a minimum of 2100 points (there is no wishful thinking involved here, this 2100 addition is guaranteed) to Roger's actual ranking points before determining the seedings. This much amount is typically easy to boost the seeding from #4 to #2. So, assuming Roger can maintain a place in top #4 (which is a reasonable assumption), he has a very high chance of being seeded as #2 in Wimbledon 2016.
If he wins Wimbledon this year, the addition will be 2900. If he wins Halle 2016 as well, the addition will be 3400. That kind of addition is likely to fetch him #2 seed as long as he can maintain a top 10 ranking. So, while there are no guarantees, it is highly likely that Fed will get a #2 seed in Wimbly 2016 as well.