You need a relatively large amount of storage space for plotting, more than most RAM disks. It has proven to be more cost effective to consume SSD's than to use slower HDD's or a RAM disk.

Any idea why the minimum plot size needs to be so damn huge? Really killed the attractiveness of the whole scheme for me

If the plot were smaller there's the risk that someone could calculate plots "on the fly" within the 30-second claim window, thus reducing Chia to proof-of-work (or even breaking it entirely? the "green" paper [1] is a bit too dense for me). It's expected and planned that k will have to increase to 33 in a few years to stay ahead.

[1]: https://www.chia.net/assets/ChiaGreenPaper.pdf

Now you just need terabytes of RAM.

it is possible, the problem is just that you need around 240GiB of temporary memory