I don't think Exodus is likely to utilise an IP, personally. Thorpe Park are building the UK's tallest and fastest roller coaster, and I'd argue that that's a pretty compelling USP in itself!
Exodus is quite a stark change for Merlin in that it has a USP based on pure scale and statistics. I wouldn't be expecting any overly tenuous world's firsts or IP tie-ins, as the thing pretty much markets itself by virtue of being a UK record breaker!
Historically, Merlin have only tended to use IP themes on major coasters when the ride hardware is not especially marketable on its own. As an example, I'd argue that Saw, one of Merlin's few instances of a major coaster themed to an IP, fell into that bracket. Yes, it did have the world's steepest non-braked drop, but the inherent ride hardware itself was not that unique on its own, as the UK's 3rd Gerstlauer Euro-Fighter and not one that majorly reinvented the wheel compared to the other two. In that instance, the IP gave it a marketing boost and it paid dividends for the park.
Exodus, though, has very marketable ride hardware on its own merits, in my opinion. It's breaking both the UK height and speed records and has a layout design that's very different to that of any other coaster in the country, with some really unique and striking-looking elements.