I’m with the “do what suits you” posters. It’s your home at the moment, and from what you say, for some considerable time to come. If you feel that a walk in shower will be the best option for you, then you go ahead and do it. There’s no point worrying about “what if’s” at some distant time in the future - people who buy a property will, over time, change things to suit themselves anyway, but in the meantime, you need to do what will be the best for you.
I imagine that the plumbing will not be moved about too much, that the walk in shower will use the footprint of the existing bath? You can always take a photo of how it looks now, so that any potential buyer in the future will be able to see where the bath once was.
We are fortunate enough to have room for a separate shower and bath, but the shower isn’t one with a longer tray, it’s just a normal cubicle. However, when we redo the bathroom, we are going to have the bath out and a walk in shower with longer shower tray so that there’s room for a seat. We very rarely use the bath now, and my husband finds it quite difficult getting out of the bath so prefers the shower. We are not going to worry about some future potential buyer, but do what’s best for us.