I've seen the alert popups that metamask is on the wrong chain, but the issue that I think might confuse a lot of users when they are on the wrong chain in metamask and they go and click the "connect account" button, nothing happens. At the very least it might be good to throw that alert window up again at that point.
Better still would be to have some kind of indicator light showing that they are connected to the wrong chain, which disables the "sign in" or connect metamask button until they are on the correct chain.