I don't necessarily think the park needs a new family coaster immediately, but more family rides especially flat rides, a transport ride, a dark ride or a flying theater. Something other than a coaster, but yes, down the line I think a new family coaster would be welcomed. I certainly agree though, a giga being the major coaster after IG seems like a great way to balance out the lineup of major thrills. It doesn't seem like IG is going to have a huge focus on airtime, so an airtime filled coaster would be a good addition.
They certainly have the space to do so in the Jungala area, it can go alongside the ponds they have behind Jungala, similar to how Mako goes over the water. If they really wanted to, they could fit an entire new area (Asian or Indian themed) in the area behind Tigris over where the Black Spot house is used for HOS. But that's a little bit of stretch right now.
I think if the next five years after IG could look something like this, the park would be a lot more diverse.
2021: S&S Screamin' Swing in Jungala (at the very least also have Phoniex back up and running)
2022: Replace Turn it Up! with a new show (one actually themed to the nature/animal theme of the park)
2023: Indoor Flying Theater
2024: B&M Giga
2025: Some kind of leisure ride, like a boat ride