I have almost every type of bathroom configuration here.
What you want to offer does depend on your demographic. Here are some thoughts....
I have 2 simple, one piece steam showers and they were very popular with all guests. They also function as a regular shower. You push one button to turn on the steam generator. They have a shower seat and 2 built in soap/shampoo shelves. Single lever hardware. Glass shower doors. Get easy to clean shower glass for any shower unit you put in!! Those rooms also have a 2 person jetted tub. Men preferred the steam showers.
I have 3 large 2 person jetted tubs in our 2nd house. (Those baths also have some type of separate shower stall.) They were there when we bought the house and although they're made by MTI, I would not install them myself since they're not self-flushing. 2 of them also have a hand held shower - definitely get that hardware if you get large tubs as it will help you when you are cleaning them! They take a HUGE amount of time and water to clean properly. Romantic getaways, weddings, anniversaries, and even many tired biz travelers and sports enthusiasts LOVED the 2 person tubs. If you have the 2 person tubs, I think you need to have a separate shower option as well.
We also have a couple of air tubs which I personally love. It's more of a bubble experience versus getting beaten up with a water jet.
And, they do not hold water in the lines since it's an air system. I have one single person jetted tub/shower combination (space constraints in that bathroom) and it was pretty popular. That was actually my most booked room but it also had the only KIng size bed and people liked the decor a lot.
Our least booked room was the one with the original clawfoot tub & shower surround. Probably because of all the other options available. Lots of older folks can't step up into the clawfoot tub. I will say that the old fashioned type porcelain shower head is amazing! One guest said it was the best shower she ever had. If you have a clawfoot tub, you need the overhead shower or a separate shower stall, with a separate shower preferable. There are plenty of folks that like the old-fashioned clawfoot tubs if it's not narrow or short.
Water supply....We have a separate hot water heater for each room with the 2 person tubs but if we were doing it, we would have gone tankless. So our 2nd house actually has 4 hot water heaters (the 4th is for the kitchen and laundry). We're getting ready to convert our personal home from 2 large hot water heaters to a tankless system sometime this year because of the energy savings and rebate. We have 4 1/2 baths. If you go this route, be sure that you have an experienced plumber who installs the appropriate pipe in order to have enough flow rate. When we renovated our upstairs and put in 3 bathrooms, we had him put the pipe in place to install a whole house tankless system down the road. No one here was familiar with the tankless systems 6 years ago. (We live in a time warp! haha!)
Good luck!!.