I would never stop a player who is going to be in the game now from playing a character they want to play... on the off-chance someone later might want to play a character that could be similar. That is slapping the hand of the player you have just to please a player you don't have and might never have. That seems short-sighted to me.I don't think it is a good idea to use houserules like that. 1. The fighter does bot get +3 AC for switching to dex.
2. You never know if at some point somone else will play a melee class and then you might find yourself in a bad spot: do you give the other person also some extra or do you live with disbalance and possible dissatisfaction from the other classes player.
3. The restriction prevents elven accuracy working with rage wgich might be too easy. At least you can't use it with GWM - 5/+10 on top as there is no heavy finesse weapon.
Overall changing such rules might have consequences lated that you did not forsee. Often one houserule leads to anontger and you wonder why the game fell apart.
The nice thing about houserules is that you can just tell your player "These are house rules I am putting in for you. Please bear in mind I reserve the right to adjust them as we go along if we find my eyeballed balance ends up being a little off." And I'm fairly certain the player will be fine with that caveat, as it means they are getting to play something they want that they ordinarily would not.