Many relatively affordable long lenses in various mounts that have been released over the past 2-3 years, such as the Tamron/Sigma 150-600s, Nikon 200-500, Pany Leica 100-400, Oly 300, Canon 100-400 II. Coupled with cameras like 7D2 and the upcoming D500.
Pity the a6300 doesnt have a good native long lens option yet. I dont count the 70-200 GM coupled with a 2x TC as an option since that combo would cost a kidney too.
Nonetheless I feel the barriers to entry have really been lowered. Granted most of the affordable lens options are 'good light' lenses which means that the big primes with FF cameras still have a role to play. More people are now able to join in the fun. However this also means that whenever there is something notable to shoot, many people would be massed at these spots which may have a negative impact on the environment itself if we are not careful.