Okay so, we all pretty much know that Blaze's appearance in Next-gen was both a huge plothole, completely random, and unexplained. No doubt it was done to "please" all her fans who wanted to see her in the first Sonic goes Next-gen installment. It's so incredibly unbelievable even the Sonic Next-gen website says that she's actually from another dimension.
Either way, the story itself suffered from the constant time-traveling. Despite that, today's question is who could've easily replaced Blaze to not only make the story make sense but added a bit of creativity to it that could've possibly made it a bit longer.
MY vote goes to Vector for reasons I'm about to explain. (Un-needed warning right there).
Not just because he's awesome (but that defidently IS a reason) but the prospect of being in Soleanna with an actual purpose (which isn't hard to come up with for Vector as it is for a few of the other Sonic characters like Knuckles) leaves room open for more story possibilities. Vector, instead of being there to deliver some message and have his reason for sticking around terminated and confusingly weird at the prospect of continuing to hang out for no reason when he has something to protect (That would be Knuckles) would instead be there on a mission with his team.
Having scattered around Soleanna they went on seperate ventures to complete a job for another mystery caller. Then shortly after Elise was captured they begin altering their agenda to see if they should try to help save the princess. Of course, Vector, being the charmer he is vollenteers for the position while the other two get the boring jobs. Their jobs turn out not to be so boring after all they get into a scuffle that lands Espio beaten and Charmy gone.
Vector of course doesn't find this out, not knowing the intensity of the job they've taken on, and starts to look for clues on the princess, then he runs into Silver. Certain things Silver says then leads Vector to believe Sonic's the one causing the city so much trouble and decides to help for the time being.
The rest is a work in progress but it was meant as a more reasoning type of thing then anything else.