Luckily for Luke all the players around him in the rankings were born in '93 so there is a very high chance Luke will be number 1 in the world next year during the AO once the '93 born players are removed from the rankings. Although junior success is good I personally think that Luke should exclusively play the junior Grand Slams next year and forget about every other juniors tournament to play futures/challengers.
Yeah, Luke is very likely going to be number one early next year, year-end number only means slightly more than former number one when it comes to juniors so it's no biggie that he lost in the quarters.
He should definitely only play the four junior Grand Slams next year. He turns 18 on February 1st so that's more than enough juniors.