I have several, with varying degrees of possibility.
I'd love to travel to London's gunmaker district and get fitted for a double, or two. Maybe a 28ga and a 12ga built on gauge-appropriate frames. I would decide after touring the various makers which one I would use. Maybe throw in a double rifle in a metric chambering appropriate to medium game to boot. No bigger than a 9x74R, probably smaller. (I scratched this particular itch as much as I could a few years ago when I bought a Merkel 280, 28ga double. It is a sweetheart but one is never enough.)
I would also love to have a small collection of original Colt percussion revolver, cartridge conversions of varying models.
Something that I may end up actually doing within the next couple years is another custom sixgun. This time I'll go all-out! It would be a Ruger Bisley, chambered in a five-shot .500S&W 1.4", sport a 4¾" octagon barrel with Colt SAA ejector and housing, custom post front sight with gold bars inlaid, set into an integral base, flat-top conversion with Bowen target rear sight, custom #5 basepin, half cock conversion, 2lb trigger (straightened), hand polished, engraved in a traditional rose and scroll pattern at about 50% coverage, bone charcoal color case hardened receiver, gate, hammer and trigger with the rest carbona blued. It will be stocked in exhibition grade French walnut or elephant ivory. Top it off with some floral carved custom leather. If I really wanted to go buckwild I'd do a sleeved damascus barrel but that adds several hundred dollars to the cost. The good part is that it will be my everything sixgun. A year or two after having it completed half the finish will be worn off from handling, shooting and holstering it. Costs too much to leave it languishing on a shelf.