I get the impression that Prezi Next is averse to starting with a blank template in part because it wants the developer to begin with preset font and color settings which the developer-chosen template makes immediately apparent. If the template is blank, the developer can’t immediately see what fonts and colors are associated with it.
More generally, the intent of Prezi Next seems to be to make the development of a Prezi “simpler” by removing capabilities and choices supported by Prezi Classic. Prezi Next, for example, does not seem to permit the developer to create (what used to be called) “frames” that, once created, might be excluded from the delivered presentation without actually deleting them and their content from the Prezi itself. Also, there is no way to “group” content items so they can be copied or moved as a unit.
So Prezi Classic has more capabilities, while Prezi Next cuts down on those capabilities to make the development of a Prezi “simpler.”
I wonder if Prezi Classic will continue to be supported into the indefinite future? It seems both the Classic and the Next approach have legitimate places in the scheme of things. I am finding that Next, once gotten used to, has some real advantages (though some drawbacks as well). The idea of pre-establishing a “planet” path structure that can be easily extended, but not in a completely free-form way, actually “works for me.”