ProphetSword
Explorer
My players are currently 14th level. I allowed both feats and multiclassing in the game I run.
The outcome is that the feats that were taken do some occasional cool things, but don't break the game in any significant way. And no one has multiclassed at all, despite having the option. 5th Edition makes it appealing to stick with your class. Even if they did multiclass, it would be unlikely they would break the game.
So allow them or don't. I think you'll find the experience to be the same each way, unless you have a min/max power-god in your group who likes to break things just to watch you squirm.
The outcome is that the feats that were taken do some occasional cool things, but don't break the game in any significant way. And no one has multiclassed at all, despite having the option. 5th Edition makes it appealing to stick with your class. Even if they did multiclass, it would be unlikely they would break the game.
So allow them or don't. I think you'll find the experience to be the same each way, unless you have a min/max power-god in your group who likes to break things just to watch you squirm.