The game has not been at level 50 for 3 years.
SE has so far taken a LOT of precautions to make sure that the FF14 disaster does not happen again so why would they jeopardize that to cater to the minority?
As much as you want to deny it, ARR is FFXIV V2.0, it is as simple as that, just as there was a 1.19 or 1,23. This is not like FFXIII-2 or Crisis Core.
The longer the game sits at level 50, the harder it will be not just for the players, but for SE as the developers, just look at the clusterfuck that was FFXI going from lv80 to 99.
If the level cap is raised gradually after 6 months, ok after a year so some people won't be overwhelmed by having to go through different dungeons for 10 more levels and get new items.
People will be become complacent by sitting at level 50 and will become attached to their primal weapons and floor 1 items from the CT/LoB. If more dungeons, boss fights or raid floors are added at level 50 the game will be stalled, the only progression will be through outdating old items without having any real character progress.
However if the cap is raised promptly, classes and jobs will continue to progress, they will learn more abilities and traits, the gameplay will improve and become deeper, and the same will happen to the old 50 items regardless of moving on or staying at that cap, this game won't have sidegrades like FFXI, it will mostly move forward, not something entirely of my liking since I believe there should be a middle ground.
People will get angry regardless of what SE does or not, you would just be foolish to believe they won't otherwise. Just look at the previous page and the posts about both the summons size and the flashy effects.
Probably 9 months before a new Job is introduced accompanied by the level being raised. 2.1 will focus on housing, 2.2 on Frontline the RvR, 2.3 will be the time for the new job and cap increase, accompany that with the PS4/DX11 release, and you have a new push for ARR around June next year.