The Meg has more going for the sequel possibility than just it's box office, The Meg is based on a book by Steve Alten who has written five more books with an sixth to come down the road in The Meg series. There is a lots of material to go on so even if they weren't to follow the books exactly they still have a lot to take from.
Considering The Meg is closing in on Godzilla 2014's worldwide take, and Godzilla's big following, it could be said this film deserves a sequel. The biggest drawback is some may feel shark films are "played out", but The Meg has been successful despite that, another negative is the Jaws films, the first was a major blockbuster but the sequels slowly went downhill and Hollywood seems to be getting cautious with sequels to big budget films due to a number of failures.
With the success of the Monsterverse (Godzilla, Kong) franchise, Jurassic World franchise, and films like Rampage, The Meg could certainly continue the trend of success in giant monster/dino films as long as it continues with what has made it a hit so far, Alten hopes so, and we certainly hope so too.
"The thing about the book series is, I just finished book 6, Meg: Generation, and each book ups the ante a little bit more. So if the producers, and [producer] Belle Avery especially I know she will follow the sequels. If they follow the sequels then they won't have to reinvent the wheel. Because it takes it to new places and introduces new monsters. A lot of people like dinosaurs, and I did, too, growing up. But the sea creature monsters and dinosaurs are much more fearsome than the land creatures. There's the T-Rex, but that is pretty much all you really have on the land. In the ocean you have some amazing sea creatures, and I'd love to see them all brought back to life." - Alten (via Cinemablend).