I do think that this story is largely nonsensical.
I sincerely doubt that Senior royals want Lord Frederick Windsor's wedding to be a "mature affair." Lord Frederick Windsor is an on-the-fringe royal. He and his sister, Lady Gabriella, are the ones who stand on the extreme ends of group photographs. Lord Frederick's parents are royal. He is not. He does not and will not carry out official engagements. He and his wife will be invited to only a few royal events, such as a major royal wedding. They will probably appear on Buckingham Palace's balcony after the Trooping the Colour. But that's about it.
Lord Frederick's children will have no titles.
If you are considering going to Hampton Court to catch a glimpse of the bridal couple, do not bother. The Palace will be closed for the day.