The dress will certainly have sleeves of some sort. It is historically not the done thing to have bare shoulders in church and for our Royal family that would be a big faux pas. I think there will be a train; if you are getting married in Westminster Abbey or St Pauls you need some kind of statement dress. A designer called Issa has been mentioned but I'm doubtful as the engagement dress was from that designer and they like to spread it about a bit. Bound to be a British fashion house I think, especially after the hoo ha after Diana once wore a Frenchie.