I believe he mentioned SODIMM RAM, so that suggests user upgradability to 64GB.I'm not so sure the new Mini will kill the value of the 2012. It will depend on how upgradeable it is. If the SSDs and RAM are soldered, the new Mini's reception could be quite cool.
The SSD will be fixed though given the T2. That limitation is balanced to a large extent with the four TB3 ports though -- add a TB3 NVMe SSD with likely very little speed impact vs internal. https://www.anandtech.com/show/13276/the-samsung-portable-ssd-x5-review-thunderbolt-3-and-nvme-/2