I dounno about that personally, alot of the categories that exist in the SM64 Extension boards arn't even possible on the Switch and it feels really arkward to be given an option to submit to a category with a platform that isn't capable of following it's requirements.
I think it would make more sense to have the 3D All Stars community create their own extensions board that eliminates all confusion between the different intricacies each game has compared to it's original release - not to mention that would work better for the Galaxy community as it seems like Switch may become the ideal way to play for them in a harmonised leaderboard.
No, I doubt it will be added to regular CE. If 3DAS gets CE LBs then maybe.
Perhaps just as a platform to select and not as a category. So if you run say 70 star CCC, you can run it on Switch and submit it to the 70 star CCC board as a run on Switch. For the main board (70 and 120 star), you might have to find a different solution.
Some categories, like All Red Coin Stars or All Coins, might be interesting under the restriction of no BLJs. For that, a subcategory allowing any version but no BLJs could make sense if there appear runs
iQue has their own leaderboards, so not a great example to use (https://www.speedrun.com/sm64ique)
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