I am very much -1 on this proposal on several grounds:
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The entire premise of this proposal is that separators do not provide value to humans. This is not obviously true and I would like to see some evidence to defend this position.
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As you point out in your 'exceptions' section, the Swift grammar relies on juxtaposition and sequencing as part of the existing grammar. This is a source breaking change for at least some cases.
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Taking this significantly restricts future evolution of the language, by taking away juxtaposition from the expression grammar. This is extremely problematic for me given the early development of the Swift language. We should not be pouring sugar in as tasty mortar to fill the grammatical cracks in the Swift building - we need to be able to drop entirely new bricks into the language in the future, and that sugar will get in the way, and make evolution much more difficult.
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This is trivial sugar with almost no benefit. The only precedented discussions we have had along these lines have been about allowing an extra comma at the end of an argument list (to allow copy and paste) and those have been extremely controversial to say the least. I don't see why we'd go completely the opposite way and take away all separators.
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I suspect that this will significantly regress QoI on error diagnostics in common cases in the user/IDE experience.