The community is more valuable than the code, because the community writes the code. So being cut off from the community is a major blow to a fork, and substantially increases their work burden.
Your fork isn't a significant amount of work, unless they've really threaded in the must-be-in-Elm-Kernel check throughout the entire compiler. Versus trying to rewrite your dependency in Elm rather than enabling importing JS, enabling JS is likely to be simpler since the functionality already exists to let Kernel modules do it.