Streaming on it's own has minimal impact on performance requirements when compared to the other components of Roon, particularly EQ, so I wouldn't worry about it either way.
The answer will largely depend on your use of EQ, use of add on products, and to a lesser degree, library size and how dynamic it is - frequent changes will drive reindexing. In my case, I have a library of approximately 40000 songs (stored on another device), stream Qobuz, and lightly utilize EQ. My i3 NUC rarely goes over 15% CPU usage and I've never had any performance issues with the setup.
If you use processor intensive add ons like HQPlayer, an i5 NUC would be the minimum CPU and I'd recommend an I7.