Yes that's what i've heard... but at least they would work better than nothing. With 'real' Dreamcast ones long gone I just kind of assumed i'd never enjoy any head to head gaming on the system...
So if a good quality of cable could be made, yes this would be TOTALLY worth it. I have 5 Dreamcasts currently and i'd probably want at least 3 cables - since I don't expect much future remanufacturing of such retro gear. If the price is lower than I expect, getting one or two beyond that is likely.