IVS is going to work out if everyone switches to always use it by default, but it's currently only used for special cases where the desired letter shape diverges from language default(the "bridge-shaped high" cases) rather than the-default and I don't see a perfect IVS world happening.
I mean, it's clearly tied to languages, so I think only viable options are either we split languages into separate tables into those reserved-for-unknown-reasons planes, or add a font selector instruction like ":flag_tw: :right_arrow: 今天是晴天 :left_arrow:", OR, if there's going to be a WWIII and one or more of Zh-Hans or ja-JP becomes obsolete, it's going to be not an important issue.
I mean, it's clearly tied to languages, so I think only viable options are either we split languages into separate tables into those reserved-for-unknown-reasons planes, or add a font selector instruction like ":flag_tw: :right_arrow: 今天是晴天 :left_arrow:", OR, if there's going to be a WWIII and one or more of Zh-Hans or ja-JP becomes obsolete, it's going to be not an important issue.