How would you weld and merge the Classic and Reboot worlds in a manner that is consistent with elements of either universe.
When an author or creator takes two previously unrelated works and puts them into a single, shared continuity.
Sci-fi and fantasy authors don't always write all their novels in the same continuity. A budding new author's first published book might be about space pirates in the 27th century, while his sophomore effort might instead be about 21st century scientists reverse-engineering a flying saucer. In response to popular demand, he might end up writing a sequel to one, or even both of these novels. Flash forward about 20 years — the author has grown wealthy from writing stories about Captain Flash Orangebeard and Dr. Smith of Mars, but he's running out of ideas and the two long-running series are in danger of getting stale. What does he do to keep the public's interest, and breathe new life into the storylines?
Combine them!
Many long-lived genre authors tend to resort to Canon Welding, usually at a later point in their career. They combine two or more distinct series they've created into a single continuity. This isn't just a one-off Crossover; for series with radically different premises, the foundations of one or both stories can be altered forever.
By combining the two series together, the author can introduce fans of one series to characters they may not be familiar with, inducing them to go out and buy the works in that series, and hopefully attract high sales from fans of both storylines. When done well, it can add a more epic feel to the tale, explore aspects of the two storylines not previously delved into, and make lots of money for the author and his publisher (and there are many examples of this, perhaps most famously The Lord of the Rings). When done poorly, especially with stories with radically different settings or styles, it looks and feels like a shallow money-grab and can potentially be a shark-jumping moment for both series.