Not sure if it can be considered a MITM attack, but without subresource integrity the developers have to blindly trust the Pika CDN to host the same script file on that URL.

SRI might be impossible to implement in this case, not only because of the Differential Serving feature but the fact, based on their examples, that developers should link to the major versions of projects, which would mean that the content under the URL will change.

This is where a reliable IPFS-like CDN would shine.