Can it serve the interests of justice? Yes
The law is not some game where the accused is given a sporting chance to avoid punishment for his wrongdoings (and the duty of the prosecutor is not to seek conviction at all costs, and police officers never lie...).
Is there an argument that it is unfair on the criminal? Yes. However, unless the court are particularly sympathetic, I can't see them not re-opening.
If sentencing is done by the same bench that decide to re-open, I would not be surprised if they were more sympathetic to any otherwise marginal exceptional hardship plea.
As regards the unfair/double jeopardy argument - I would expect it to carry more weight if it can be shown that the defendant had changed his position (analogue with estoppel), or that to disqualify him for 6 months now would be a harsher punishment than if they had done so (subject to exceptional hardship) at the time.
The potential issue with arguing that the court are not fit for purpose, is that you might need to invite the bench to recuse themselves. If you can make a distinction between the bench and the court staff (whether underfunded and overworked, or incompetent and arrogant), that might garner more sympathy.
