But honestly, I actually don't think that's much of a big deal. The difference between taking a venous draw and doing a finger stick as not as big of a deal as Theranos made it out to be.
If instead Theranos had a small, portable analysis machine that could work with small volumes of venous blood, and they had a big deal with Walgreens to use that together with things like low, up-front pricing for tests, I think that still would have been a great advance. Note there are startups like Everlywell basically trying to make that vision (cheap, accessible, up-front pricing for medical tests) possible.
Obviously there are huge challenges to designing such an implanted medical device, and it could only ever work for a limited set of assays, but I expect something like that will eventually be possible. We already see diabetics wearing continuous glucose monitors, which gives a preview of how such implanted sensors might operate.