It would be interesting if in the future technologies were introduced that permitted mining extreme bodies like neutron stars. Or a least, mining things like carbon planets or gas giants for diamonds, metallic hydrogen and suchlike. I doubt anyone would actually wish to mine neutronium. It's actually a liquid and a very poor material for armour despite it's persistent portrayal as an inpenetrable solid in Star Trek. And for one thing, that neutronium door in TNG would not only weigh many millions of tons and instantly sink to a planet's core, it would be extremely unstable and likely to spontaeously explode!