It seems that for major occasions, such as weddings, the requirement is for royalty to wear the most eye catching outfit which probably rules out the RAF No1 uniform!
In the run up to the wedding I joined in the speculation that he might appear in a surprise reintroduction of the pre-war RAF full dress, which was quite swish (although NOT with the very silly hat!) There was a precedent, as his great grandfather, King George VI (then The Duke of York) married in this uniform in 1923.