Mixed media is incorporated into the standard categories.
A paper model which is single media (paper) would qualify for Single Media/Basic Kit Build category. Two months ago at Omaha there was a paper model entered in SMO, but the entrant added wood and metal (and cited the materials with the entry sheet) forcing it to one of the standard categories. Single Media Only!
If you want a separate paper category at the national level there need to be 8 to 10 entries by 8 to 10 separate modelers over 3+ years. Why separate modelers? The national rules prohibit sweeps - you win one award per category. If you enter multiple kits, yours are judged first to determine your best - then that one goes up against the other entries. Once I had to evaluate 15 battleships by the same guy, then had his best go against another 9 entries in a category of 24, and if I remember he didn't place.
The contest committee tracks entries for changes in trends that support new categories. We generally look back 3 to 5 years for trends. We have often been asked to add a wooden ship category. There are so few entered that the numbers do not support a separate category from the existing sailing ship (all material) category. The most that I can remember is three all by the same guy, then he was bummed that the rules prohibit sweeps - that and he was beat by better entries. You still need to meet the overall organization's judging criteria. Bigger does not always mean better. Adding things does not always mean better - there is more to screw up. The competition committee once added a commercial category in response to requests and what had shown up on the table. Entries dwindled so that the last year there were but two, by the same guy. The category was eliminated due to lack of support, The support needs to be on going.
Local contests are not bound by national categories and may not adhere closely to national rules. Get traction there.
IPMS-USA/NCC Head Ship Judge