CMV (if you have this view; otherwise, a reply of agreement would be much appreciated to reinforce the point): "one should have the optionality to apply to both Oxford and Cambridge for one's undergraduate degree.
UCAS's decision to force you to select one or the other is entirely arbitrary without any reasonable justification. Your life is on the line.
A sample size of 1 lends itself to an extremely considerable luck factor in the interview process. Hell, even a hypothetical sample size of 2 with both Oxford and Cambridge is very low and reduces that factor by the square root of 2 (mathematical approximation as IID is not a reasonable assumption). In the US, it is common for elite students to apply to approximately a dozen top universities to reduce the standard error of luck in undergraduate admissions.
Gaining admissions to either Oxford or Cambridge undergraduate will result in a much better life perpetually until death. I am 33 and can attest empirically to this fact. Status as an Oxbridge alumnus is perpetual and relevant decades after graduation. Again, we are speaking life or death.
In my case, I attended Cambridge for my undergraduate studies, initially as a CompSci in the 1st year and a Physical NatSci in the 2nd and 3rd years. I achieved 2:1/1st/1st. I then attended Oxford for my Master's to gain the "double crown". I did not apply to a Cambridge Master's because I already had the Cambridge brand, notwithstanding I could have stayed on for a 4th year if I wanted to for an integrated Cambridge Master's.
In my UCAS form, I only applied to Cambridge. I would rather not attend university than attend a non-Oxbridge UK university. Fortunately, I was lucky and was admitted. Had I been rejected, I would have reapplied the next year and the algorithm is recursive in that each reapplication is for a less selective course in a less selective college until the algorithm ends up with Land Economy at Girton. In my case, I do not doubt I would have any problems gaining admission to Land Economy at Girton. My plan (1, ∞] would be to apply to HYPS + MIT + Caltech in the US concurrently (I am American and went to a British international secondary school).
While I had top UMS scores (including a 100%), so do the vast majority of people who apply. I will admit that I was lucky in the interview process in that I interviewed abroad and the interviewers were strapped for time alongside easier competition. I quickly developed rapport with the interviewers with jokes and they low-balled me with two nearly identical mathematical questions, with the interview spanning only one hour. On another day with a different set of circumstances, I could have very well been rejected.
As a former Master's student at Oxford, the caliber of Master's students is considerably lower than that of my undergraduate cohort, with the degrees being significantly less selective (and you can apply to both, as you should!). There were plenty of Oxbridge rejects who did a Master's at Oxbridge to have the Oxbridge name on the CV. I do not consider Master's-only Oxbridge alumni to be Oxbridge alumni.
If the ability to process almost double the number of applications is a problem, money solves everything in life. One and the best solution would be to increase the application fee by whatever threshold amount required and use that money to manage the increased required throughput.
Because of the central limit theorem, inter alia, lopsidedness risk resulting from a preference for either Oxford or Cambridge for people who are accepted into both is negligible. Oxford and Cambridge are equally desirable and therefore should have hypothetically comparable cross-yields to the point of negligible difference.
To caveat, this post is not satire. The points may come across as overly elitist and dramatic, but given my life experiences to date at 33, again, I can attest to the gravity of the situation. Further, we are in an Oxbridge forum.
Summarizing, we need reform and that reform is a trivial algorithm. And to quote ABBA, "I love the feeling in the air. My kind of people everywhere."
Enjoy!