Apart from BAE flogging their kit, I don't see what the point of this exercise is. There is zero chance of this being built by the UK, which can barely afford the nuke subs it has which are its main military threat.
> The important thing about the new concept is that it will illustrate a direction of travel and many of those technologies that will be embodied in that will first see their service through the Typhoon
https://www.gov.uk/government/publications/combat-air-strate...
A large part of it is about supporting the high-tech manufacturing industry in the UK, so it creates good jobs, attracts investment, can compete for exports, etc.
Turkey and India are trying to develop fighters as well, the UK has the tech to build these, there are markets.
The Tempest looked interesting, until I saw the hoping to fly by 2035 part, which really means 2040 or later.
It's really a technology make-work project to keep their skills up and retain defense capability, which isn't a terrible idea so long as the cost is tightly contained.