When an emergency reduces either House of Congress below quorum,
state governments can respond with temporary replacements
faster than special elections can be held.
Although the kind of emergency this answers may never happen, the section adds significant power to the states when the government would be weak and especially vulnerable to possible abuse.
This is an exception to the text's balance of state and United States powers
and must be given serious consideration.
What section 4 adds to states' powers
balances a potential reduction of state powers
although they don't alter any text regarding this balance.
It isn't necessary for an amendment to retain any particular balance of powers
but it's best to balance losses with gains.
And preserving the continuity of government takes precedence.