For what it's worth, I dislike loose ends, too, although this isn't a major one. I'd like to see it acknowledged somewhere, even if it's only an affirmation of Sci
's apathy (
) - a throw-away comment letting us know the matter was resolved offscreen (or is somehow being investigated). The "Andorian Crisis" arc is over now (I'm very impressed that it sustained a decade's worth of stories), and that's the only real dangling plot point I can think of - especially since it implied that factions within the Andorian intelligence service had been co-opted by the Tholians, meaning it's slightly more meaningful than "we have a few duplicates around".
I also agree with KingDaniel
that exploring the potential uses and misuses of transporter duplication could be interesting - there's a lot of potential there, particularly for exploring dilemmas rather unique to the setting.
PS: I must admit to preferring dedicated follow-ups wherever possible; my only real complaint about the otherwise fantastic Full Circle,
for instance, was that the Changeling arc was dropped so rapidly and concluded offscreen.