I would certainly hope that Elton John will not be singing that song at Prince William's wedding.....I also hope that there are no performing dogs, trapeze acts, magic tricks, or drink/food vendors walking up and down the aisles during the ceremony at the Abbey.
Prince William may be the "new" face of the royal family, but the Abbey is a CHURCH.,...and a wedding is a solemn religious rite.....it is NOT Dancing With The Stars....or an occasion to spotlight aging rock stars wearing pink glasses and singing any of their "best hits from the 90's".
Of course, the Queen is getting on in years and is certainly more than weary of strife inside her family....she may be so thankful that William is marrying someone nice...and not Paris Hilton.....that she will weigh his adherence to Windsor standards as far as mate selection goes....and allow him to do pretty much whatever he wants with the ceremony.
I just hope the whole day goes well, and that the end of the day finds everyone in good spirits, and no untoward events having occurred during the day.
EDIT: Though I do think the Queen and Prince Charles will try to go along with whatever William's wishes are about the ceremony....I am pretty certain that, no matter how much William MAY wish it, The Earl Spencer will not be allowed to make any public speeches at either the wedding or the wedding reception.
All of the royal family have had QUITE ENOUGH of the Earl Spencer and anything he might wish to say.