I can see Spong having some good wins in MMA, possibly in the UFC before long due to name value.
It's not like a pro wrestler or footballer dipping in MMA, Spong is a very good fighter who has been training with top MMArtists like Overeem and Evans for a while now.
The name of his game WILL be sprawl n brawl, he's with the right people to learn how to fend off grapplers, he's young and athletic. Notice his very wide stance at the start of his MMA debut.
If he wins his next few fights, he'll also carry massive fear factor. We all know he's no submission fighter, and his striking is advanced to the point that most MMA fighters will feel pressured to take him down. That fear and pressure will win Spong fights, because as soon as he defends one takedown or starts landing his strikes, most guys will wilt. Another advantage he has is sheer experience, the kid has many fights under his belt. In kickboxing yes, but the point is, he's very used to getting in the ring and fighting, many crossover athletes do not have this.
We'll see though.