Just to be clear, the name of the word is supposed to be read like "shbosh" or "shboash". Native languages often use ⟨X⟩ for what English uses ⟨SH⟩, because it's what Spanish used to do back then.
Or as in older Spanish varieties. Around 1500 or so Spanish phonology was considerably similar to the one of Portuguese, but then a bunch of changes affected the fricatives - like Spanish [ʃ] becoming [x] (from "ship" to "loch"). That likely happened to increase the distinction between [s] and [ʃ], there was a "gap" in the phonology (no back of mouth fricative) left behind by Latin [h] kicking the bucket, and Spanish filled it.
Eventually for most Portuguese speakers the same "gap" would be filled too, but with another consonant - [r] becoming stuff like [ʀ ʁ x χ h ɦ]. So the chance that Portuguese [ʃ] follows the same path is slim at best. (I say "most" because some Gaúcho, Sulista and Caipira Portuguese speakers still use the old style trill. Myself do it sometimes, but for me it alternates between [r] and [h].)