Well that's just is, isn't it? It doesn't exist yet... So yeah, they'd have to build it.
They wouldn't be limited to "existing dining options." Making DAK an all-day park would require more than just bringing in a nighttime show. They would also need more dining and more attractions. Avatar will cover some of the need, but there would be additional work as well.
Wishes is one of the highest rated entertainment options in guest surveys. If it changes, it will likely be a reworked fireworks show but will still probably be "traditional" fireworks sans any water effects, special projections, etc.