I don't think the issue with Lobo is CGI. The issue with Lobo is how to portray the character for the movie market and how to write a workable script. While I love the Lobo's Back style comics, let's be honest here...a lot of Lobo's 'canon' (I kind of cringe while saying that) doesn't even make sense. It was never meant to, and that's part of why I loved it. Even though a lot of it seemed to be this strange melange of pubescent teen T&A and gratuitous violence, I was able to put that aside along with any expectation of the comics making any sense. But anyone arguing for that iteration of Lobo is going to have a hard time explaining how some of those storylines would translate into a successful movie.
I think you can still pull off a 'classic' metal-style Lobo (GTFO with that New 52 bullshit), but you would probably need to pull back and write the story more along the lines of LEGION/REBELS or his generic 'bounty hunter' image. And even though I liked LEGION/REBELS, that's even more obscure than GOTG to a lot of fans and I don't see DC going there, so'generic space bounty hunter'it is.
I think Momoa would be perfect for Lobo, but honestly don't know if him playing more than one DC character would put people off. Maybe no one would really notice, other than by seeing his name in the credits? I will say though that I think they should consider using Lobo as more of a cameo villain in a larger movie first before trying a standalone movie. He's perfect for that - he can fight an entire team like GOTG to a standstill w/o having to worry about dying (lol), or even go toe-to-toe with a lot of supers. Done properly, you could probably leave the entire "Lobo" situation unresolved ("Is he dead? Will he be back? We kicked him out the airlock...can he breathe in a vacuum?") or give him a side-story MacGuffin that lets him come in, fight [insert character here] and then fly away (like "I was hired to recover this X they stole from my client, it was nice beating your ass Supes, we'll tango another time").
The saddest part for me is that one of his most classic beat-down victims (Lanterns) are in the'fuck that movie was terribad'purgatory, and who knows when DC will take another shot at that.