There is mention of one issue - melting of the tips. They are working on modifying the collector to reduce the stress on the emitter, which suggests that a prac

There is mention of one issue - melting of the tips. They are working on modifying the collector to reduce the stress on the emitter, which suggests that a practical device will not be reversible. (from a sufficiently abstract point of view, transistors appear to be reversible too, but in practice they are not.)