I think that Great Wolf Lodge is prevalent enough in all parts of the country that there really isn't much demand for long distance travel to Orlando for a similar experience.
The core of Great Wolf Lodge's business model is short weekend getaways for people who live in the relative vicinity - nobody is flying across the county to visit one (or something comparable) when the same outcome can be achieved with only a few hours drive.
Perhaps Universal could make some improvements on theming over what GWL does, but the practical constraints of being indoors (floor space, height, etc.) will prevent them from having anything near the grand scale or large, thrilling rides that Volcano Bay has. Because of this, I think that Universal trying to build an indoor waterpark would be a massive mistake.
I think there could be a case for including a small indoor waterpark (activity pool, short lazy river, a few slides) in the next big family-oriented value resort, along with a normal outdoor area. That would allow them get in on GWL's business a little bit while providing additional and more consistent entertainment options for families who won't be spending as much time in the theme parks.