Usually soffits exist b/c they have ducting and wiring in them, first check for that, my neighbor had his gc look into the walls with a small camera.

(and you have to really search the whole soffit.... during a previous project when the wall behind the kitchen was ripped out, the contractor said my soffit was empty. luckily, i didnt believe him and 2 years later ordered cabinets not to go all the way to the ceiling... sure enough during demo there was some plumbing that really couldnt be moved. same contractor, he was embarrassed.)

thats not to say your soffits cannot be framed smaller than how they are now.

i'm not understanding what shelves you are considering putting below your cabinets, do you have an inspiration pic?

If you are ripping out would you consider leaving soffits as is as they might not be movable. and instead turn the U shape kitchen into an L shape with a long island....if you have the width. If soffits are removable then yes new cabinets would be very nice indeed.

We have our HVAC rework soffit locations often to give our clients optimal design in kitchen reno's. It does involve more work but is certainly doable in most scenarios and the return of beautiful tall cabinets with expanded storage is always worth it! That space would look lovely with some tall cabinetry worked in, good luck!