And if it's made to fit into Classics, more modern classics aesthetics are probably a good idea.
Personally speaking, I prefer toys to have a more modern detailed sculpt. I am not fond of the simplistic cartoon aesthetics. For example, I am a fan of Mastermind Creations because their toys offer both the nostalgia in the overall design but also modernizes it with nicely detailed sculpts and aesthetics. To me, traditional cartoon aesthetics are way too kiddish.
Something that I have learned over the years is that the primary factor that sets the 'tone' or 'personality' of the overall design is the head sculpt. If that doesn't look right, it will affect the rest of the toy. For me, the head sculpt as it is now is too cartoony and reminds me too much of Animated rather than G1. Due to this, I don't see SkyGuardian in it's current form fitting Classics very well or Masterpiece for that matter. It would just look odd when displayed with those toys.
As it has been mentioned, every person will give you their own personal views on how it should be. You have to be able to take an artistic and commercial position on what you want this toy to be and stick with it. It is ok to take suggestions here and there that you think are appropriate or work better but you have to maintain your own artistic focus.