^Yeah, I very much agree with the points Sad made. I'd be down with Swert's proposal if "artistic representation" can include previously made 3d masks, in case those creators want to have a go at it, and so we can have the opportunity to skip waiting on the artistic representation being printed. In that scenario, if the modeler is the one submitting the entry, I don't see a reason to worry about them jacking up the price since if they were to win and do that, someone else could come in and make a replica for a better price since the design itself has become canon.
Eh, art contests have usually been relegated to characters who play a minor role and there's no real excuse to make a fully fledged moc for (e.g. Surel, Kirbraz, Nikila, etc). The Toa Hagah, even apart from their Rahaga counterparts, play too large a role in the story to relegate to mere art. Tbh, I think that would be a far better option for some serial-only characters like Yesterday Quest Toa or an actual Kestora depiction, for example.
Now, although I'm inclined toward the hard non-CCBS camp, it seems apparent that a compromise will have to be reached, and after mulling it over, I want to present a proposal. Although for me a restriction on HF and G2 elements would be favorable, personally, there's already a precedent as to, for example, the inclusion of the technic pieces of lines that had gone before--not only in official contests, but in the sets themselves. A hard ban on CCBS might not be necessarily very fair.
I suggest, then, that although a general ratio should be put forth (and, even if not strictly enforced, should remain in the minds of the voters). However, certain pieces that are central to the identity of the respective themes of HF, G2, and other sets using constraction should be completely off-limits.
Take Hero Factory, for example, where the crux of the theme is the Heroes. From the beginning, they were generally built with distinctive pieces to differentiate them from their Bionicle predecessors. This distinction should be respected--so no hero helmets, Hero Cores (or chest pieces with Hero Cores), Hero weapons, or printed pieces that are central to the identity of those heroes, etc. Same with the villain pieces, for the most part, although since these characters were less central to the line, it's more difficult to give a hard "no" (heck the original big boss, Von Nebula, used a Hydraxon helmet, for example--as did, at one point, the big bad they were building up toward the end). So I don't see so much of a necessity to outright ban villain pieces, but even their use should be done with respect to what fits and what doesn't in the world of Bionicle--I generally think a lot of their masks would fit fairly well and look pretty interesting. But for the Heroes themselves, their pieces should remain unique, as highlights of their identity.
For G2, the masks, above all, were the central core of the theme, and to a somewhat lesser extent, the weapons, the printed armor pieces, the Skull Spiders/Shadow Traps, etc. Not only those of the Toa, but even the Protectors, Creatures, and villains of the wave, as they played far more unique roles in the story (be it individually or together as armies--I'd go so far as to argue even their respective roles significantly eclipsed those of the HF villains for HF). I would strongly object, therefore, if someone were to use the G2 Mask of Creation (or Control) for Artakha, since that Mask of Creation is so central to the theme--not to mention being the focal point of 2015's whole marketing campaign. To steal that Mask of Creation outright would be to strip G2 of that special piece--not to mention the Mask of Creation has G2 language inscribed on it. While this would admittedly match the description we have of it, I still think any G1 Mask of Creation should, at the most, draw influence from it or pay homage to it, rather than just copying and pasting.
For Chima, Star Wars, Superheroes, mech, Ben 10, and whatever else uses constraction pieces (idk lol) then this would translate to the heads or pieces shaped like fur (Chima) or distinctive weapons, or printed pieces that designate identity, or whatever else. Again, Bionicle never needed Chima pieces or HF 3.0 pieces to build sick looking Rahi, so there's no real reason to start.
In general, though, I think that the central pieces of these respective lines should be off-limits so as to maintain their individuality. Some of these pieces are what give these lines flavors and life, and to go and raid all of these for the sake of a competition feels wrong. These special pieces are made with their line and its unique aesthetic in mind, not that of Bionicle--not to mention, I doubt there will ever be a moccing situation where a Furno helmet makes or breaks a moc. His XL cape, maybe, but certainly not his helmet.
tl;dr: generic pieces good (within ratio/moderation/reason), character-centric pieces bad