As postcards are often associated with places people have travelled too, I can see this idea working when the predominate aspect / feature of the image is that of a local scene particular to the place / area it is promoting and then the more general scenes as above would probably sell well beside them.

I think it a brilliant idea, I can visualise the town / city / street name in the centre and the featured land mark replacing the large tree in the shot shown above. You obviously enjoy the challenge in your panoplanets; go for it Take a sample into the high street somewhere and see what response you get from the shopkeepers selling postcards, or better still sign a deal with a chainstore of some sort, or a postcard producer with the distribution network in place, and work your way around the country.

As you all ready have a website of examples, write, email the postcard card manufactures today (while your idea is effectively electronically, independantly dated, be aware less honourable often pinch other's ideas)- I would also put a © watermark on editions, images published online too - Best of luck.