Very concerned about the long-term viability of this experiment.
Don't be concerned. Even if the "unknown" increases and reached 100%, it is extremely healthy, and was the
normal state of affairs before mining pools were invented! Unknown miners are unknown to each other and can't collude. Yes, you can have a big secretive miner, like 18xf3MQ, but several exist today anyway.
You don't know and can't know that they are unknown
to each other only that they are unknown to the person constructing the chart. For all we know "unknown" might be a single miner, or 90% of it might be a single miner. In fact that isn't extraordinarily unlikely given that most truly independent miners use known pools.