A very interesting idea to try and achieve upsell to people who would normally consider business class as being too expensive.
I’m not convinced it will work, but maybe that is just because I didn’t think of it myself! It can be booked online, but you have to do it via the complex itinerary page which I suspect most travellers rarely actually use for non-stopover multi-segment itineraries.
It certainly is a novel idea, and so long as it doesn’t kill O&D availability for last minute minute corporate travellers wanting business class over both segments, it is probably at least worth a try.