WHILE the bods over at RTHK agonise over its post-1997 role, Craig Quick and the lads at Metro appear to have their route on the through train well mapped out. Sources tell us that as of next month Metro Plus will convert to a bilingual format similar to FM Select, except that Mandarin will replace Cantonese as the alternate lingo. Since Metro News metamorphosed into Metro Plus it has been gathering a new following, drawn by the steady diet of golden oldies. With Canto-pop a newish hybrid yet to attain nostalgia status, the balance of Chinese golden hits can only come from the world of Mandarin music. So all in all it makes sense. Besides, if Craig and his band, the New China Blues Agency, were to add a Mandarin standard or two to their repertoire they could even get themselves a cosy little slot on the Metro Plus airways.