The thinking here is that we could support the Intl API without actually tying it to any ICU in Gecko. This would reduce the security and crash surface area, as well as allow us to deploy different code and data (tables, etc) than what ships with Gecko.
I did try to build ICU with emscripten and it seems to succeed. There are some packaging steps it does that don't work, but I feel like those could be solved with a bit of effort.
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