In the guidelines for the new in-app review dialog, Google say that
Your app should not ask the user any questions before or while presenting the rating button or card, including questions about their opinion (such as “Do you like the app?”) or predictive questions (such as “Would you rate this app 5 stars”).
Since it says should, and not must not, it's not clear if it's an actual violation of some policy to go ahead and ask the user if they would like to leave a review before showing the dialog. The reasons for doing so are plenty, for example to minimize intrusion in the users workflow and let them leave a review when it's convenient for them.
However, in those guidelines it also says
calling a launchReviewFlow method might not always display a dialog.
I haven't yet had time to implement the app review dialog, but I'm guessing one could simply fall back on redirecting the user to the Play Store if the dialog won't show?
What I'm wondering is - how strict are these types of guidelines from Google? Are they more like friendly advice than Play Store policy? What could happen if one does something that is recommended against ("should")?