There have been 5 people it's happened to in the time I've been playing. 2 of them sought it, 2 of them sought to stave it off, and 1 person just didn't want anything to do with it and had it happen anyway.
It doesn't happen automatically, it's a long road, and a long winded plotline.
If you do pursue the 'become elemental' plotline, it will always end in storage if you succeed. You do not get to play an elemental. Period. (This is collective 'you', here)
Anyone can pursue this with their elementalist, but I don't personally understand why any person would want to store their fully branched magicker like that and just give up playing them.
While there are elemental races you do not get your coded race changed at any point, nor do you receive any actual 'perk', as it were, before you are far enough along the path to be stored. You know the thing where you're watching like, your mate and kid get all upset because you look at them like they had two heads when one of them uses your 'love' to try to implore you to do something. They ought to know better, elementals don't love. etc.
While people may have gotten to rp things like that out in the past, before you're getting any new powers or a new race, now, you're stored. Yes there is rp to be had, but usually just in the shape of losing all your ties and emotions and coming untethered from everyone around you (mostly internal rp, heh).
I've heard of/know of/seen it happen to 3 people since 2009. Musashi, who it appeared from the posts about it on the staff boards, did not want it. My pc Nil/Kruth/Ayani, who was terrified of it happening (and later killed herself to avoid the transformation ever being complete). And a vivaduan named Wik/Malwik. Who also wasn't seeking it. Who also got stored/died before any actual coded differences came in to separate them from a regular fully branched elementalist, afaik.
Alkyone, Sanvean's whiran, might have been different. It might have happened to others before that and been more powerful, but imo, going elemental is like dragging out a storage request longer than necessary because you're bored playing your fully maxed pc, or, in the cases of those I've seen, having it forced on you 2/3 of the time, even.