Using the same keystore across multiple services is sharing private key. Spreading this habit will end up in drama with a probability of 100%.
If someone use the same private key with N applications, it takes only 1-of-N to have a flaw for the fund to disappear. This goes against the security model of asymmetric cryptography.
Keystore are useful only in case of emergency: if the service you create them with goes off, you don't loose control of your funds. However, once you load it into a new application you're supposed to move all the funds to a new address or to change signers.
Don't make it into a cheap login solution please.