And there are plenty of people here, in this thread, who would gladly do the design for FREE.
Design is easy. Then you need to test, meet FCC emissions requirements, all worldwide standards, thermal, acoustics, etc. Update the pubs, update all of your marketing material, web pages, dealer stock. Retool manufacturing, supply chain updates, etc. Stock replacement parts, train tech support, train the sales teams. And more that I've forgotten.
I want a new Mini, I won't buy a mini until the new one is released, but product release is not cheap. I used to work at a big hardware company and you should have seen the engineer's faces when I told them their fully functional prototype would take 2 years to get to market. I think things are a little faster now but there is still a lot of work once design is complete.