I am glad you made this comment about the MiG 31 so I didn't have to, lol.

Fancy schmancy j58 turbo "ram" jet with convoluted design that has two different afterburner / bypass loop modes, with crazy air bypass/recycling plumbing?

Nah, fuck that.

Just make the entire engines out of titanium and nickel, we have a lot of that shit in Siberia, and, use a fuck off huge heat exchanger system in the single bypass loop.

Also, this quote:

During the flight research period, two aircraft were lost - the first prototype and the first production one. There were no casualties, and this, in comparison with the results of other machines being created, was quite a good indicator.

• ENGINES OF RUSSIAN COMBAT AIRCRAFT by Kotelnikov V. R., Khrobystova O. V., Zrelov V. A., Ponomarev V. A. (Mediarost, 2020)

https://www.secretprojects.co.uk/threads/secrets-of-the-d-30f6-turbofan.44489/

Apparently this is where you go when you're too old to know what a 'Warthunder' is, lol.