The lion's share of the test volume is done by commercial labs like LabCorp and Quest, who don't care that much about designing their own tests, they just want to maximize patient volume.
One of the companies I used to work for had a large chemistry system that could be run "open" but only a few customers used it that way, a couple research laboratories and I think a winery. Thousands of other instruments were used for plain ol' medical testing.
Even if you designed a sufficiently open system that could run Roche or Siemens reagents or whatever, any problem with the reagents and the company will just shrug and say "it's not our instrument, no guarantees."
One of the companies I used to work for had a large chemistry system that could be run "open" but only a few customers used it that way, a couple research laboratories and I think a winery. Thousands of other instruments were used for plain ol' medical testing.
Even if you designed a sufficiently open system that could run Roche or Siemens reagents or whatever, any problem with the reagents and the company will just shrug and say "it's not our instrument, no guarantees."