If you can configure your laundry so that you dryer is on top of your washing machine and open a doorway between the laundry and bathroom (in the wall between where your shower and toilet current is) using a sliding door you'd be able to close off the current doorway for the bathroom and then add a bath along where the doorway and shower is, keep your laundry separate for user ease and avoid moving plumbing (which is expensive). That way you can have a shower over the bath and have both a bath and shower option in that bathroom. My best advice is to go and get some grid paper and drawer your bathroom to scale taking into account the size of all the features you require to make sure that they fit (cut samples out to scale and you can play with arranging things. Remember too that standard doors take up more space within the rooms then sliding (either external or pocket) doors and moving plumbing is expensive so if it's a short term deal before major renos take place avoid it.

Your mockup scheme is similar to our master bathroom we just completed - photo below. I know you mentioned storage being a concern - our mirrored cabinet has offered an amazing amount of storage in a very small space and also helps bounce light around. I was worried about black taps etc too so we kept chrome fixtures but added in a matte black candle and black potted orchid to create a similar effect which we can change out later on. Our floor tiles are dark but because they are semi-polished they actually bounce around a lot of light and don't make the room feel dark if that is a concern. We also have a huge fiddle leaf fig in the corner (not pictured) which adds a really nice feel to the space - a plant like that could help bring in the outside greenery in your bathroom. Instead of the storage tower you have to the left of the vanity could you do say some floating wood shelving, possibly with baskets added for more hidden storage? You could also bring in the 60s theme with what you displayed on there eg. photos as you mentioned? In regards to the window - a previous house we lived in had a window at about shoulder height in the shower - as well as letting in heaps of light it was amazing for storing toiletries etc!

agree with bigreader ...the slidingglass doors look good in the exhibition homes but the space between the sliding door and the last cabinet or washer will be awkward to keep clean and a great place for lost sox but it depends on the size of the laundry...if there's enough space for the cabinetry to go right up to the external wall as well as having a sliding glass door that can avoid the odd gap but need the room will need to be at least 2.5m deep and how do you create privacy for the sliding door?...i prefer a hinged glass door and small window for light and ventilation without exposing all my laundry mess to the world and simple venetians maintain light and privacy

my suggestion includes moving the toilet to gain access to handwashing and tall storage... everything else is standard sizes which will be cheaper and easier to install than special sizes or walk in showers (eg the laundry benches are available at the major hardware stores and could easily be installed by a handyperson with a small drop in sink (unless you need to hand wash huge items which can be hand washed in a bath) the small sink that will allow more counter and under bench space and make sure that the plumber installs all the taps and WM connections under the counter and has all the pipes installed at the back of the space to allow for a tall laundry basket to squeeze under the bench)