I'm surprised that people want Taika Waititi as a replacement. Love Ragnaok or hate it, it's a vastly different movie than Guardians. A lot of people just see "bright colors and space-stuff" and think "it's like Guardians". It only resembles Guardians superficially.
Guardians' humor is scripted in advanced and timed. Ragnarok's humor is ad-libbed and improvised.
Guardians' visual style is mostly realistic designs and practical effects. A lot of grit. Ragnarok's is much more cartoony and exaggerated. Less of an emphasis on photo-realism and creating a "lived-in world".
Guardians is influenced by late '70s/early '80s Star Wars-style space-operas. (Semi-serious, with the orchestral score and whatnot). Ragnarok is influenced by later '80s Flash Gordon-style sci-fi (much more over-the-top and cornball, complete with synth.)
I just don't see the two as compatible. Personally, I vastly prefer Guardians' style (although I have come to respect what Waititi was trying to do). I have a feeling a Taika Waititi GOTG would just come across as a cheap knockoff (I mean, the style he's mimicking is essentially a cheap knockoff of the style Gunn's mimicking). Maybe Taika Waititi could mimic Gunn's style, but I'm not convinced.