Well, shame on me. I've been doing it for 3 years on a daily basis.
I have my RAM drive rsynched to an SSD partition that is the same-ish size.
And here's one area where you're incorrect. Safari loads web pages. Each page loads javascript. Many of these leak over time or simply never purge their contents. I often end up with 8 GB used in Safari. Safari alone is a citizen that doesn't play by these rules because each page that loads is a prisoner of the javascript that loads and often doesn't handle memory freeing properly.
When I use my RAM as a drive, I get near INSTANT builds on OS X.
This matters to me more than your claims of "all modern operating systems taking full advantage of the RAM". If the operating system takes full advantage of the RAM, it may not be to my best benefit.
For example, Apple apps now by default do not quit when you close the last document. They merely stay in memory, hide the UI and then need to be relaunched to enable the UI again. Why does this matter? For TextEdit, if I want to open a document form the open menu if I close the last document and click elsewhere, this forces me to reopen the app because the OS fake closes the app (really only hiding the UI) while the rest of the app stays memory resident.
So, I have to relaunch the app. This takes more time and ONLY just renables the UI. How much memory does this save on my 32 GB machine? 1 MB. Now, that's certainly not taking full advantage of the RAM. It's a case of the OS designers thinking that "he wanted to quit the app, so we'll do it for him". But I didn't want to quit the app. The computer is not taking full advantage of the RAM in this case. That's not what I wanted it to do.
Maybe I have apps in the background that are doing stuff, but I want them to pause completely if another app is running in the foreground. Maybe I want ALL Safari pages to suspend their javascript when in the background, but the app still can still process downloads as if it's running at normal priority.
See, there are many cases where the computer's OS will not take proper advantage of the RAM and the processing power since it can not mirror the user's intentions. Even in cases where it tries to, it often gets them wrong. And in some cases where it does (Safari javascript), the computer ends up eating processing power and RAM for tasks that the user doesn't want it to be placing priority on. And in some of these cases, it can't allocate RAM and processing power properly, because it can't if it relies on other programmers writing their javascript competently and acting as good citizens.
I can cordon off a small chunk of my computer's RAM (since I have way more than enough) and direct it to do pretty damn much just want I want it to do.
That's why I bought it. I don't want the OS to prioritize things the way it wants to. I want to tell (parts of) the OS to prioritize things the way I want it to.
Cheers.