No one needs 256GB. No one even needs 128GB - the only reason why you'd truly need large storage is if you want to work with files that require that space - for example, if you work with a 40GB file, then yes, you'd need at least 128GB.
What it really brings is convenience. Without the extra space, you're going to have to spend time every once in a while to clear up things if you like to install lots of apps or load up lots of movies.
On the other hand, needing 4GB of RAM is actually something that is a lot more likely, especially if you are going to edit large movies or graphics images with lots of layers. At the moment, this isn't a common use case because you don't have full blown photo or video editing apps, or 3D rendering apps on the iPad, but it could be something that happens in the future.
At that point you might just want to get the next iPad Pro though, because you're probably also going to need lots of computing power.
EDIT: After thinking about it, even RAM is avoidable - Apple could implement memory page swapping on Flash storage, but performance would suffer as a result. I'd definitely not recommend it as an option - it's going to be a lot more inconvenient than clearing out files every once in a while.