To provide good advice we need a floor plan with dimensions. Graph paper with each 1/4" square = 6" is usually sufficent.

Would I be inviting problems with water remaining on the floor?

Do you mean water sitting on the floor of the shower? If you have the appropriate slope towards the drain, water should not remain. Or, do you mean water on the floor outside of the shower? The correctly designed shower should not leave water on your floor either.

Do you think of this as a forever home where aging in place is a consideration? If so, I'd make a walk in shower in a heartbeat that is easier to walk in to than your current shower.

I meant water sitting on the floor of the shower daily. This is our forever home until the next step - I am in my 70's now.

I prefer to not remove the glass block window. I provides good lighting and privacy.

I would guess that the column could come out. I can see where removing the closet would open up that area.

Why in the world do you think you need a larger shower? The space could be improved upon. It certainly has that late 80s vibe going on.

I'm in my 70s and would want a stable seat for the shower, a handheld sprayer, grab bars because I lose my balance for no reason whatsoever these days, something easy to clean. A shower 9 ft wide takes a long time to heat up. Unless the seat is on the side you cannot sit and reach the water at the same time.

But I would not give up a tub, especially in an upscale home like yours. The older I get the more I like the idea of the shower with three tiled walls and a glass door. It's easier to install those necessary grab bars.

You could keep the shower the same size and make the entry more accessible.

Remove the linen storage and put drawers in your vanity cabinet and a dressing vanity under the window with more storage