Wouldn't it be better to have a more open competition?
For example "Monstrous Creature", "Warrior-size", "Special Character" or "Flyer".
I believe this would make for a competition with more diversity in the entries and, most importantly, more entries. I don't know about the rest of you but what I enjoy the most about these competitions is seeing all the entries and getting inspired for future conversions.
The last competitions 9 entries show that making a niche character like the parasite, though fun, is not a model that most people plan on making. (Note that I know that the tervigon had a lot of entries, something I attribute to the fact that the tervigon is a very useful unit that most want to include in their lists, unlike the parasite). Units like the Swarmlord or tyrannofex are also a bit too "niche" since they are both units that are financially expensive to make and most useful in games of 2000pts or more, leaving out the people who have just started their army and might be building their first 1000pts.
However, if the category would be say "Monstrous Creature" the new players could enter a fex/tervigon/trygon, the veterans who already have a couple of thousand points can build a Swarmlord and those who feel like it can convert a MC non-combatant and enter.
This would also not leave out the "old" units or units that have models. Just because the trygon and the carnifex have models doesn't mean they can't make for kick-ass conversions, as this forum has proven many times
So in short: More open competition - > more freedom -> more entries - > more kick-ass models - > everybody wins