Is a new iPad mini expected soon?

Apple generally doesn’t pre-announce new devices or device models.

Contributors here are all end-users, just like you. Other than information published by Apple, nobody here has any insight into Apple’s product design decisions or future software development roadmap. The Terms of Use that govern participation within the Apple Support Community disallows speculation as to unannounced or future products.

Whatever iPad you buy, now or in the future, it will eventually be replaced with a newer/faster/better model. As such, the best time to buy a new device is when you need it. Attempting to second-guess the product release program is folly.

think best you can do is to look at the release dates and timespan between them

iPad Mini - Wikipedia