There have been a lot of suggestions so far, but here go a few based on things that I either have, have added, or plan to add, etc..
1, Steps my pool was built with only ladders, it now has drop in steps, next time the liner gets changed I may go with something more permanent.
2, Nearby changing room, more than 1 would be nice, my pool building has a bathroom with shower that is about 6x10 ft, lack of changing place and people using the bath room/shower always leads to lines, if I had it to do over I would put the toilet and sink in one room and shower in another.
3, Good lighting, modern LED fixtures are revolutionizing options here, the traditional one light in the deep end is not as good, better would be multiple smaller lights.
4, Automatic cleaner, I have used suction side cleaners for years, and just invested in my first robot vacuum, any automatic cleaner beats doing it the old fashioned manual way.
5, some sort of food prep/serving area near the pool, nothing makes people hungry like swimming
Ike
p.s. think a long time before getting a diving board, is it a must have for you, my pool has one, but it is 30+ years old when it seemed all pools had diving boards and over the years has been the cause of more than one accident requiring medical attention including one case with a teen age girl clipping the bottom of the slope to the deep end mouth first and ripping a finger length hole in the liner with her braces (thankfully she did not loose any teeth).