I had been interested in the same thing as well, and for some time, had been following this 1 and only thread I could ever find of someone actually taking on the challenge. In the end, he threw in the towel. He is just one guy, I would imagine with this core of his work being available online and the crew of brainiac's around here, people intimately familiar with the inner workings of the software, they could very likely bridge the gap.
Having said that, though a fun and exciting challenge, I would say "WHY?!". Very likely the market share of these WD MyCloud EX product lines are pretty small and not worth the time and effort. I have an EX2, EX2 Ultra, but ultimately ditched them for their lackluster performance and application support, but got them for $99 so it was my initial stepping stone on my way to XPenology. I had tried sooooo many other things, RockStore, Windows Home Server, Open Media Vault, FreeNAS. Most of those other Linux based OS solutions are excessively over complicated, too many levels of annoying granularity that much be configured just to do the smallest of things. I'm an IT professional for over 20 years, and just found those solutions to be undesirable. Just setting up something simple like TimeMachine share, if you didn't know you needed to go into 10+ menu options/levels, only to have it NOT work - frustrating. Synology software, straight forward, clean, intuitive and "it just works".
Still, in case you want to go to town on it, you might like this:
https://community.wd.com/t/alternative-firmware-debian-jessie-synology-dsm6/156551
Cheers!