I must admit that I love how proficiency works in 5E, simple and lite. With wiggle room like the Rogues the two skills they get to double their proficiency bonus on.
This got me thinking about additional training with regards to proficiency. I don't want to steal the rogues thunder and give other classes that big of a boost to skills, but having a rule for additional training would be nice. It could also be used in instances where the character gets the same skill from two different sources like say class and background.
I'm planning a game which will use only the (free) basic rules and some home brew subclasses. In that game I'm going to try out these house rules.
All characters at creation can pick out one skill to be specialized in. This skill nets an additional +1. If two character options give the same skill twice, that skill also becomes specialized and gains a +1. If the skill gained twice is also chosen as the one specialized skill then that skill is double specialized and gets a +2 instead. These bonuses all stack with proficiency bonus.
I'll see how this works.