Of we were to design an HE system from scratch on 2025 I don't think we would start with 2 elite universities and build round that. I suppose you could argue Oxbridge is literally the result of British history rather than some overarching HE policy of a modern governent.
If you ask any minister about HE they never differentiate between universities but just state political standard fare, 'engines of the economy, opportunities for young people, supporting local communities etc.'. Oxbridge actually just be quite difficult to deal with from a modern educational department when society is much more egalitarian than 100 years ago.
I wonder to what extent career outcomes are still largely dependent on family wealth and connections rather than university? Are there students at Oxbridge (and others) who because of their relatively poor backgrounds do find it difficult to seek out the same range of opportunities as their wealthier peers or simply wish to go back to this or home communities and do something altruistic like teaching with their degree?