I'd get rid of it, and open the area up, or keep it .. I wouldn't do a pony wall, they're never soild enough.

I plan to do as Sophie has suggested. Creates an excellent location to tuck away the family sized bottle of Head & Shoulders! A nice frameless glass door will make for a fresh updated look.

I agree with the comments, it is not a large opening i would skip the knee wall and open the area up.

No knee wall. Either leave it and do like Sophie suggested, or take it down completely.

Aside from any curb that is a part of your shower design for holding your glass sliding doors and/or water control, don't add any knee wall or pony wall. If you want privacy, use different glass doors. Even adding suitable curtains outside the glass doors would be preferable to half walls.