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Or making a decision based on what they want and what may well be better in the future, this being a custom frame that'll likely outlast any parts on it. Whatever the reason for the decision it doesn't really matter, they've asked a specific question and have already said they don't want adaptors, unless it was impossible or really stupid to not use adaptors, then the answers shouldn't really be about them.
Why have a solution to a problem which is caused by making the wrong decision in the first place?
Why not make avoid making the wrong decision and not have a solution as it won't be needed?