That will be a very interesting one, for decades now we have just replaced our Hercs with the latest model due as much to lack of alternatives as anything(operational req allowed for the C-17 Buy) but this time it looks like its going to be a very open Market with the A400, KC-390, C-2 all possibly on the Market and I would not right the Herc of yet.
I expect it to be in the next DWP/IIP due mid 20s.
Luckily for you guys you have the option and availability of using C17 and now C27 (in numbers) so therefore have a range of platforms to cover so the old adage of if it ain't broke don't fix can still apply as the C130 in well and truely still a relevant asset. Us on the other hand need to be more selective as both type (singular) and numbers play a vital part in our overall thinking.