We've had a model image of the Panther Clipper floating about for far longer than, say, the Krait model was shown before it was introduced.
So why haven't we seen the ship itself before now? (If indeed we do see it now.)
Here's what I think the problem is:
If the ship doesn't have vastly more cargo capacity than the T9 or Cutter, players will be bitterly disappointed.
But if it does have, say, twice the capacity of those ships, then the amount of money you can make from simple loop trading will also double, perhaps approaching Cr30-36m/hr.
The devs aren't notoriously fond of deliberately introducing new sources of easy money into the game.
It may be for this reason, rather than any problem with the technical design of the ship, that the Panther Clipper hasn't appeared yet and never may.
Make it an Imperial exploration ship.