There is nothing challenging or costly about tooling for parts like this.
They may not be challenging but having spoken at some length with a company that makes moulds for and moulds polyrene they are expensive to produce (
I was looking at producing a product in polystyrene some years ago -
I abandoned the project because the cost, when everything was factored in, made it too expensive fot the market it was intended for).
The principle problem that you would face with the proposed hive is that your market place is limited.
1. The WBC is really only found in the UK.
2. You are only looking at beekeepers who want the aesthetics of a WBC and are prepared to pay for it - you are not looking at a 'new' WBC - it's an imitation.
3. Often people who go down the WBC Route do it because they like the traditional nature of it - polystyrene may not altogether meet their requirements.
4. You are competing with a fair number of existing suppliers of polystyrene hives - all of whom have their proponents - they may look like fish boxes but they work, they are cheap and practical.
5. You will need at least two variants - I like 14 x 12 frames - but a large number of beekeepers prefer standard nationals and a growing number Langstroth hives. More moulds, more stock, more costs.
If you take all the above into account and start estimating how many you would be able to sell - and factor into account the cost of the mouldings, the premium that small production runs dictate and the costs of getting it to market I rather think that it's a commercially flawed proposition. Although, as an esoteric exercise I can see the appeal.