A client has an existing successful website that sells niche products - they are well known in their marketplace. They have two sets of key customers, let's call them (a) and (b), that need addressing in different ways to maximise sales. (a) is the more specialist end of the market, where people have complex needs - there are fewer of them but repeat business is likely, and we can talk to them in more technical language. (b) is the layman's end of the market - there is a vast pool of potential customers but they'll be more casual buyers and need to be addressed more in layman's terms.
So what they want to do is to take their existing website, and essentially split it into two different websites, one for each market. The one that will use the existing domain, with all the links that have built up over the years pointing to it, will be the site for the more specialist end of the market (a). The domain name suits it better, which is why he wants to use the existing domain with that site and not the other.
(b) will be a brand new domain. The client will write new product descriptions across the board so that the two sets of product information are not duplicate.
I'd rather he didn't do this at all, because of the risk involved, and the difficulty of building up the traffic to the new site, which is after all the one with the best chance of mass market sales. But given that the client has decided that this is definitely what he wants, does anyone have any thoughts on what the action plan should be?