Bitcoin has technically changed over time yes, but it's identity is clear. Bitcoin having changed over time doesn't mean that any additional change is valid.

The appeal is not to the exact written text of the white paper, but to the explicit identity of the technology. It is a cash system. That's why people like it, that's why people use it. In terms of storing and transmitting multi-media, there's much more appropriate and better ways.

This mirrors the legal concept known as the "spirit of the law": the meaning of the law when it was written. Following the law literally can sometimes violate the spirit in which is was written.

The spirit of Bitcoin is as the title of the paper suggests. If we wind up going from a "cash system" to "multi-media system", we've made a wrong turn. Putting multi media on Bitcoin simply because you can is violating the spirit of Bitcoin.

To use a crude analogy:

You could encode image data into a series of electronic bank transfer "reference" fields by breaking it up into tiny chunks and making a lot of transfers. It's obvious to anyone that this is not the point of those fields. Violating the intent of the system is how we categorize "hacks" from proper use.

Appealing to the identity of a bank as a "financial institution" is not invalidated by the mere fact that banking has evolved over time or that people can hack it.