I've been thinking along the lines of the clear acrylic albums and the sewing into the page protector...if it would be possible to make a postcard size pocket (sort of like a wallet photo holder) and somehow attach it to the lo through the page protector and have it hinged so you would first see the front, and then could flip it to read the back. This would protect the postcard and the lo. Anything like a postcard size wallet photo holder out there?
What about using the page protectors that are made for 6, 4x6 photos? The ones I use are 12x12 size, and I put pics in some of the pockets and cardstock with journaling in other pockets. If you don't put anything behind the postcard, you can see both sides.