A revived speech and a shifting global backdrop. Beijing is signalling new urgency in its push to elevate the yuan - but the trade-offs remain unresolved, analysts say.   SHANGHAI: Chinese President Xi Jinping wants the yuan to become a global reserve currency - one that central banks hold in significant quantities, a role which the US dollar has dominated since the Second World War. The ambition is not new. China launched cross-border yuan trade settlement in 2009 and secured the currency's