kmcg - Good point about the safety bars. If this for an elderly you probably should install grab bars even with a walk in shower. We did that too for my MIL. Also, be sure to check your local codes about the drain. Some allow 1-1/2" drains as since many of us use low flow showers now it's not a problem. I have put a rubber flat stopper over mine some times when I feel I need a foot bath. Even after washing may hair etc, it doesn't get close to overflowing.

That alcove is designed to house a tub only, not a tub shower unit. You can't "repurpose" what's there without water damage to your floor, window, and behind your walls. The tub itself not designed to be used that way, and neither is the window designed to be in a wet area. You'd need to rip it all out and start over by installing a smaller and waterproof window, then installing a tub that had an integral tile flange which is part of the waterproofing system needed. Then your waterproofing membrane and whatever wall cladding you might want.

I wouldn't give up the tub because it really makes the bathroom. I think the Master Bath is more of a master with a soaking tub. I would never give up 2 sinks. It wouldn't be good for our marriage to be fighting over the sink. I like the privacy of the toilet area in your first drawing. I would go with the smaller shower with the tub. I have had a 36" by 36" shower for years. A 6'2' large build husband, who is comfortable in there. We are going to make our new shower 36" x 48" because we have the space. I agree with someone else don't put the bench seat in. I think tile also gives you more space as opposed to a fiberglass surround which adds a couple inches to the interior walls. I considered going into my closet for a 60" shower but I don't think it is worth it. I will make the smaller shower elegant and put top features in it.

How imminent is possible resale? What are typical buyers' family make-ups in your area? Are no-tub homes common in your area? Is it a buyers' or sellers' market? Unless resale is in under 5 years, average age of kids in the neighbourhood is under 10, everyone has tubs, and it's a buyer's market, which is an unlikely combo, LOSE the tub. Too many people hang on to them because it's believed we 'should'. A good walk-in shower with a built-in seat and large enough for a wheelchair is far more versatile and practical. It's not just stepping over the tub rim that makes people want to get rid of them. Tubs are far smaller, often messier, & less commfortable overall. And you have an outdoors one for the luxury aspect. We need to LIVE in our homes fully, not under the shadows preceeding future owners :)