Nope, 50 coins max per day, no matter how many hours, days and weeks your mon has been in the gym, the daily limit rules.
So keep in mind that if you have already got the 50 coins for that day and a mon nearby is low on motivation you should try to feed him in order to make him stay at least until 00.00 granting you 50 coins, because if not he will come back to you with nothing.
This is for the biggest flaw of this system, not the limitation of 50 coins, the limitation that anything past that 9 hours is USELESS, and you don't have any power to control it, for example calling the mon back yourself.
This leads to no sense of taking down and control multiple gyms like before, which leads to a faster stagnation than ever (increased because prestige is gone), people normally don't want/like other teams to get coins, so they leave their gyms for days and weeks, the place gets distributed fast, for example if you have 9 gyms, 3 gyms per team (just an example), no one attacks because you have no reason to do so, and if you do it people go there and kicks you out in less than you get even 2 or 3 coins, so you learn the lesson and don't spend time and resources on taking down gyms.
I am seeing this on my town since day 3/4 of the rework, the first days the hype was high and people didn't know how the system works, but now this is the situation here and on the 4 towns nearby. It is a shame.