While I love the idea, I also don't know if it's feasible.
As I understand it, this is Imeo's hobby, which would supposedly mean it's not his main profession (I could be mistaken, but that's how it comes across to me). No more of that if he goes all-custom.
Also, consider the cost for getting multiples of everything in different materials, needing different machines to work them, etc etc etc.
Consider the wait time. No mod, even "built-to-order" mods, have that degree of customization, and still, people wait a couple months for their Chucks and SuperT's, which are not highly customizable (the picture finished on the Chucks probably isn't any more difficult than a regular finish, which is why it doesn't cost more). With that much customization, and the demand, you could be waiting 6 months for your GG.
If the vendors were putting the pieces together, consider the time delay in shipping when they have to choose from possibly hundreds of custom parts to get your order right, and they have hundreds of other, non-GG items to deal with as well.
And finally, consider the reason that I landed on the GG. The price. Yes, the price. The GGTB is $75 with a telescopic battery feature, and it's built to last. Other mechanical mods with no extra features, and even missing some basic safety features, cost more, even twice as much. Even the GGTS is priced well. It's $150, but consider everything it does. He would have to at least double the price of everything - and probably triple it - if it was fully customizable.
I love the idea. I just don't know that it would work.
Although, if he can handle the extra work load, maybe he could have the option of a custom GG, for people who are willing to pay a lot more, and wait a lot longer, to get it.
But to move the entire GG line to full customization would make them totally inaccessible to anyone who isn't basically rich. Not only that, but you'd probably forget you ordered it and have gray hair by the time you finally got it.