Is there any reason I shouldn't store my keystore in version control?

Anyone with read access to your Git repo will get the private key. This is considered a security issue and for that reason it is not recommended. If your GIT repo is completely private meaning no one but you has access to it (NOT A private repo on i.e. GitHub, but rather git repo on local disk or in the infrastructure you control in 100%) then putting your private key there is as safe as keeping it on your local disk.

Assume that the keystore itself and the private keys inside both have strong passwords on them

Note that password is your last way of defense in case of your ("public") private key. If it will be compromised in any way (guessed, stolen, cracked) then it's over.

Additionally, I am more than certain that not all (if any) of devs needs access to release keys. If you need them to have it, hand it off the repo. But I'd first rethink the security policy.

To update your App you need two things:

• Access to the Google Play Developer console that owns the application.
• An APK signed with the correct keystore

By putting the certificate into your repository and sharing it with your developers you are giving up one security token.

If your Google Play Dev Console account is secure then you should be fine. But it depends on your szenario.

Putting it into the repository is much easier:

• Your repository is cloned on many places and usually backed up properly.
• Your developer team can use gradle to sign your production release automatically.

Many people prefer putting it on one or many SD Cards and put it somewhere. But most people don't have a place called "somewhere" in their office. Can it still be read in a few years?

Two more consideration:

1. If the product owner of the android app changes in your company you never know if the old owner still has a copy and nobody knows who has access to it already. You can't change the key. So if the key is once passed from one person to another, it must be assumed insecure.

2. Of course, you can keep it completely private. It is secured by your password which nobody knows. But what happens if you die? Someone might want to update your app. It is not possible. A private key which is kept private is lost when you die.

So I think putting it in your repository is fine. Take care to secure your Google account. For this account the password can be changed, two-faktor can be activated and so on.