Oh, absolutely agreed that having multiple copyright holders is the healthy way to deal with the "proprietary relicensing" problem. Not just multiple in fact, also different kinds of copyright holders (e.g. not only corporations that don't care about the code itself). Given that the initial author(s) get to choose the license, if they wanted to keep their options open, they wouldn't choose copyleft-next 0.1 anyway. So the clause might be of limited use in practice (except in special conditions; no real-world examples come to mind).