From Suzanne Gildert - Dwave System is hoping to scale along a Moore’s law like trajectory, but it is incredibly difficult with so many technical challenges of building a new processor technology. They are really hopeful that they will be able to scale to 1000, 2000…qubits. Of course like you say there is always the possibility of unknowns.
Regarding entanglement, it is something they are looking into, but there is not really a good definition of entanglement (or any ideas in the literature of how to measure it) for more than 2 qubits in an open quantum system. The physicists at D-Wave are trying to come up with more experiments to verify the quantum nature of the chip at larger and larger scales. Everything they have measured so far has agreed with quantum mechanical theory so we’re confident that it will pass future ‘tests’ too.
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