For a public CA it MAY (I doubt it) make sense to rotate signing keys "just to be safe," but again this is a matter of risk assessment, not "best practice." If one wants to argue for setting key rotation to a century or so, just in case, sure - but short of that it is adding overhead that may bite later (you have to retain the old keys as long as the data they encrypted is valuable, or you have to re-encrypt all your data every time you rotate). If you accept that passwords should be rotated every 180 days, then a key with 256 bits of entropy can be rotated every 4.6 x 10^63 days. "Rotation of signing keys." I am not aware that signing keys are cryptographically weaker than keys in general. If you have lots of older, extremely valuable data then you might want to rotate, but that is an outlier case, not the general case, and would be reflected in your risk assessment.
#Cipher key cracked
If you are rotating keys every year (AWS customer-managed KMS for example), or every three years (AWS managed KMS keys, for example) the majority of your information assets will have been touched during that period in the general case, meaning the person who cracked the key will already have them by the time you rotate. "Reducing the volume of compromised material." Theoretically yes, but practically no.
#Cipher key password
And if you can, set minimum password lengths to 16 characters or more. Say "no" to password rotation and set detective action thresholds-you will save about 1 man hours per person per year in lost productivity, and you gain a real chance of identifying an attack, rather than depending on rotation to limit its extent. I.e., For keys << than 80 bits, like 1DES, and particularly for 8-character passwords which have 47-52 bits of entropy, no frequency of key rotation is sufficient. If you depend on key rotation you will average the rotation interval divided by two of exposure.
In that case, you manually rotate keys (and if necessary algorithms) as soon as you become aware. Other than a known breach of the key, the one exception to the general case is when keys are NOT cryptographically strong, or become weak over time, or the algorithm is compromised.
It MIGHT be appropriate depending on your risk assessment, but it is not a "best practice." This is one of those cases where people assert "best practice" when in fact it's just a practice that has become a standard without any real justification. There is no practical reason to rotate keys as a matter of practice, save one, provided the keys you are using are crytographically strong to begin with.
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