We discussed this yesterday on 1:1 but today when updating I get confused a bit, so let me respond.

One assumption:
After looking at the Identity code, both login and register cause saving prekeys for a given device, and there is no need to additionally call RefreshUserPrekeys. (@varun could you confirm?).

In D9423#276980, @ashoat wrote:

However, I think we still need to do it in registerOrLogin, so that we make sure the prekey that we pass when calling the identity service is initialized (in case it is the first call)

Maybe I am missing something, but I think prekey is initialized from the beginning. Looking at types prekey() always returns string which means prekey should be defined.
I also verified this by calling createPickledOlmAccount.
So perhaps there is no result in validating on a brand new account because keys are not published yet anyway, but in this case new prekey will be updated to identity while login/register.

Just wondering if this understanding is correct.

and not expired (in case the keyserver has not been touched in some time).

I can imagine a case when we log in to identity, and have very old keys, so validating here makes sense. So I will keep the old validateAccountPrekey which only generates/forget keys and call it here (retrieveAccountKeysSet in login.js). There is no need to upload keys via RefreshUserPrekeys in those keys because it will be done by login/register.
I would also rename the function revalidateAccountPrekeys to validateAndUploadAccountPrekeys or something similar (introduced in D9421, used only for validating via cron job).

Is that okay or I am missing something?