Hmm, well... sure, as long as the writers handle it well, as with most concepts. A child can be one of THE greatest product of a two people's love for each other, and the romance between these two was a huge deal in their debut episode. However, there is one particular way I'd prefer to see it done and would give the writers infinite props if that could pull it off.
Have Shining and Cadence adopt a foal.
Already see where this is going? Yes, I'm suggesting they adopt a Changeling foal/nymph to raise as their own. The cross-species adoption trope is always an interesting concept, and yeah, there is naturally the irony of SA and Cadence adopting a member of a race whose Queen tried to destroy their lives, which would be an ever present elephant in the room. This specific concept has been attempted several times in fanfiction albeit with mixed results.
How would they find the kid? What process did they go through to decide to adopt and raise her? Well, I guess I'd leave that up to the show writers, who I'd definitely trust to pull it off.
And that doesn't at all mean Skyla has to be sidelined and forgotten; on the contrary, they could give the Royal Couple two daughters: the snarky, troublemaking Skyla and the upbeat, optimistic, sometimes naive Aphid (the changeling, duh).
And ba-ba-boom, you've got a new pair of Royal Sisters and two of the six new main characters for G5, right there.
That's my thoughts on the matter, but what about you? Do you want or think the couple should have a kid? If so, why and how would you see the concept executed? If not, why? I'm curious to hear your opinions on this.