Maybe you should read about that again, because you obviously don't know what you're talking about ;-)
The A-12/SR-71 was leaking fuel while it was sitting on the apron/ramp, because due to the insane heating that occurs at Mach 3 you have to compensate the heat contraction of your tanks and everything else. So while they do leak on the ground, as soon as they start getting anywhere close to operating speed and the structure thus heats up, everything seals shut. No leaking midflight. The Skunk Works director Ben Rich (who took over after the original director Kelly Johnson stepped down) wrote a book called "Skunk Works: A Personal Memoir of My Years at Lockheed", it's a good read.
1. That makes it even worse/more dangerous 2. Still leaks fuel midflight during large portions of the flight 3. Its not like it’s some ingenious design tradeoff - wasn’t supposed to do that (which is my point)
You mean the kind where plane literally leaks fuel mid flight? I think they're already there