I have a set of Hunday poly cush drive rubbers and they work a treat. I can guarantee there will be a huge market for them as THEY WORK.
I did look into finding someone to manufacture them a while back, but the setup cost were too much for a mere mortal like me to swallow. So well done Zen Overland (and Steve) for offering to get this one off the ground.
What I would say is that they do need to be priced carefully. Hunday's are really at the top limit of what is acceptable (mainly because they are shipped from SA), otherwise just replacing the stock ones every now and again becomes the more cost effective (especially with inner tube mod) option. I'd say double what a pattern set cost would be fair and similar to the cost of the OE parts, or course it all depends on setup cost, predicted sales and Zen's profit margin.
Maybe starting a poll would be the best way of gauging interest?