I have no idea of your style also are you thinking redoing the use inside the closets or just doing new bypass doors. If I google bypass door styles the are literally 100s so I guess I need to know what you want from us?

It seems like your efforts may be better spent improving the interior storage elements..creating more solid shelves and cubbies perhaps...as to the doors ...replacement is the only option as remodeling doors usually just hampers the function..in the office i would suggest two hanging bars on one side ..and the other side only shelving.. ..so you only need to open one door fr office materials

What is the style of the moulding and doors in the rest of the house?

Honestly, these are so plain as to be neutral, so if you're going for a clean, modern look, I'm not convinced that changing your doors will look any more modern or simple than what you currently have. Bypass doors aren't sexy, but they're functional and stay out of the way.

Install hinged doors.

In concept painting the doors ( if they are wood) , with chalk board paint ...in part ...or all ...might be useful for short term notes..reminders...etc.if they are metal ..magnets can serve a similar purpose on the outer door

Also note... heavy..or solid doors are harder to slide...require more substantial floor runners..and are famous finger smashers