The long-overdue Mac mini update looks similar on the outside, but how much has it changed on the inside? Quite a bit -- though you'll be glad to hear some things have stayed the same. iFixit has torn down the diminutive desktop, and it's evident that Apple made only very strategic changes to the system's internals. It's still relatively easy to get inside the system by popping off the bottom and sliding out the entire motherboard. And when Apple said the memory was upgradable (unlike the 2014 model), it wasn't kidding. There's a shield to prevent interference, but it's easy to remove and install your own RAM sticks.
There are plenty of changes to accommodate the 2018-era components, of course, and you might not always be a fan of what's new. The teardown shows the modern, desktop-class Intel processor, Apple's T2 co-processor and the thoroughly modern controllers. However, it also confirms that both the CPU and the solid-state drive are soldered on to the board. If you insist on having gobs of fast built-in storage or a Core i7, you'll want to order your computer that way from the factory. It's a good thing there are four Thunderbolt 3 ports to accommodate external drives and graphics, then.
All told, it looks like Apple tried to walk a fine line with the new Mac mini's guts. It provided the added power some people were looking for, but purposefully left some features untouched (or even rolled them back) in the name of pleasing server operators and other pro users.