It's basically a laptop without the keyboard, trackpad and screen - it couldn't bet that hard to release if they wanted.
Looking at the history, Mac mini has been upgraded every 18 months or less
except for the last model, which lagged by 2 years. This is the month when 2-year upgrade cycle is due, so I suspect Mac mini will either get a spec bump or retired for good.
It's not that Mac mini is hard to upgrade, although if Apple is planning more substantial upgrade, it might be one of the reasons for delay.
Let's face it. Mac mini isn't dependent on cutting edge components like iMac, MacBook, and MacBook Pro are. As sad as this may sound, it's obvious that Mac mini isn't selling in high enough quantity for Apple to bother with more frequent upgrade (Mac Pro is another example). The existing inventory must clear out and new components must arrive in sufficient quantity and profit margin for Apple to bother upgrading Mac mini.
Anyway, 2 year is the longest we had to wait for Mac mini upgrade and many signs point to Apple updating various Macs this month. Hopefully, Mac mini will be one of them as I am eyeing a purchase myself.
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I wonder if there will ever be another Mac-focused event. It may be silent refresh until the end from here on out.
Even if Apple holds a Mac event this month, and every single Macs get an update one way or another, I doubt Mac mini will receive a mention. It will instead receive a silent upgrade on the website.