You don't need to use React as a SPA, though, is what I'm saying. (When using React, those component trees, too, compile to 100% plain-ol'-functions.)

Twirl is fine, insofar as it's attached to the Play (that's not to impugn you for picking it, my history with Play is colorful and frustrating). I wouldn't raise a flag for that. But not using something in this vein definitely is, and React is probably the most accessible way to do it for the 90-95% case of developers.