To qualify what I mean by "16-bit microcomputer system", I am talking about a system that has not only a 16-bit (or 32-bit) microprocessor CPU, but also a 16-bit wide external data bus connected to the rest of the system. So, 16-bit access to its primary RAM, and the possibility of 16-bit wide access to peripherals.
To qualify as "mass-market", the system should have been generally available for purchase by consumers in quantity as a general-purpose, desktop style, computer in the vein that became popularized as "personal computers". So, no prototypes, experimental, kit, or bespoke systems. Basically a conventional microcomputer marketed to business, professional, and/or home computer users.