[webcomponents] Should shadow host have `display: block` by default? (#426)

Continuing my proposal / question in https://github.com/w3c/webcomponents/issues/224#issuecomment-193652791 here:

Do most of custom elements that have `display: block` rule attach a shadow DOM?  If so, should we make every shadow host default to use use `display: block`?

Making custom elements default to `display: block` is problematic because we have to do either:
 1. `display` value changes when an unresolved custom element becomes upgraded
 2. We change `display` value for all existing unknown elements with `-` in its name


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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/426