Hi Juho,
For the Rift boss, I am not sure if you are aware that it is supposed to be “a massive, 10-story colossus”. Also, which of the 6 planar themes (earth, fire, water, air, life, or death) are you going with?
I like those vehicle studies, and it’s awesome that you are so motivated to improve your 2d skills. I am personally going to learn 3d to break into the industry as a modeler or an animator, but I want to continue working in 2d on my own to get into concept art some day.
I went to a cg event called Anomaly last October, and one of the presentations was made by guys at ArenaNet/Futureploy. One thing they said about concept art is that “mega competitive is a mega understatement.” They actually recommended getting into the industry as a modeler and using your position within the industry to gradually switching over to 2d. If you think about it, there is no shortage of talent out there, and many amazing 2d artists get by doing freelance work.
I wish you best of luck and hope you stay motivated, but just wanted to say that getting into the game industry with 2d might be harder than doing it with 3d.