There is so little light reaching out there that you will never have a hope of imaging it (IMHO), especially if it is a dark object. although if it has any sort of heat generation in the core it might show up on IR imaging. Inference based on the behavious of known objects is probably the best choice for the forseeable future. Of course if New Horizons could be retasked and sent along the inferred orbit there might be a chance to get some data, after all it's already out there. But you'd need to be pretty sure you know where it is before redirecting New Horizon, assuming it could be redirected with the available fuel.
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