I have recently been seeing games that go well over 50 for max player size, such as Meep City. Meep City allows 120 people per server.
game.Players.MaxPlayers = 100
This is my code, and yet the max players still stays at 50. The script's parent is Workspace.
The ROBLOX Team is testing larger server sizes for members of the DevForum (https://devforum.roblox.com/). You will not be able to increase the server size to above 50 until the ROBLOX Team decides to release it to the general public.