It’s fair to say that the rumours were never as strong as for the 5. Recently there was a photo which purported to be a prototype of a Mini 6 and two iPad Pros. It was pointed out at the time that it looked like the back of a Mini 5 and in the absence of any announcement either at the event or in a press release (Air 3 and Mini 5 were in a press release at the time) it seems that that was correct. In contrast, a couple of months before the Mini 5, a backplate for a mini in the then iPad 6th gen gold emerged. The Mini 4 was a different shade of gold, suggesting that something was coming.
The expectation has mainly been because the Air 3 mirrored the Mini 5, the Air 4 was on the market and the base iPad has caught up with Mini specs (minus things like laminated screen.) But as we know Apple will do as they please and to be fair, no one expected the Mini 5 to get the A12 on launch when the A10 was in the base iPad. That gave them longer before they needed to update it again (A8 in the mini 4 was already less powerful than the A8X Air 2 it was released alongside, and showing its age at 3.5 years when the Mini 5 came out.) If Apple are mainly catering to the vertical markets with the mini then having the same processor as the base iPad will be fine, and 2 processor generations better off than they were before the Mini 5 came along.
Personally, I would not be happy to pay the £70 (I think) premium for the Mini over the base iPad, but if customers are willing to, that works for Apple for now. From memory the Mini 4 ended up being at much worse a premium than the Mini 5 is now, as the only storage available was 128GB. When I bought my Mini 5 the 8th Gen was £349 with A10 and 2GB RAM. £50 extra for an extra GB ram, 2 processor generations forward and a laminated screen (though that wasn’t a must have for me) was a steal.
If I had to buy a new iPad tomorrow, I’d get the 8th Gen and make do rather than pay full price for a Mini 5. I very much favour the Mini form factor and it helps that I have someone who would be delighted with a iPad 8 when I went back to Mini. They don’t want a Mini. In your shoes, I’d be tempted to look for a Mini on offer (there seemed to be one the other day, according to the Buyers’ Guide) but they may have disappeared since given that the 6 isn’t imminent. Or an Apple refurb if there are any available in your country. No iPad refurbs at all in the UK for a few weeks now.
I may be wrong, but I don’t see Apple letting the Mini fall behind the base model again and on that basis, I think it’ll be updated in October.