If you don't mind the russian, there are some options.
There are three books by A. N. Sokolov in russian. The first is on missile cruisers, both actual, and proposed, the second is on destroyers, both actual and proposed and the latest is specifically on never were's and alternative versions of ships actually built and/or proposed. These are not as in depth as Friedman's work and the quality of the drawings leaves something to be desired in a few cases but there is more than enough detail to get one interested and make the books worth getting.
The titles are:
Sovietskii Racketnyii Kreiser: Zigzagi Evolyutsii (Soviet Rocket Cruisers: Zigzag Evolution), Moskva, 2006
Raskhodnyii Material Flota: Minonostsyi SSSR i Rossii (XXXXX Matrerial of the Fleet: Destroyers of the USSR and Russia, I always have trouble with that first word!
), Moskva, 2007
Alternativa: Nepostroennyie Korabli Rossiisky Imperatorsky i Sovietsky Flota (Alternatives: Unbuilt Ships of the Russian Imperial and Soviet Fleets), Moskva, 2008
These first three shouldn't be hard to find. I got mine through Russia-on-line, which is based in Maryland.
Taifun Magazine also published a special on "Super Destroyers of the Soviet Navy" which deals mostly with traditional gun-torpedo destroyers and leaders that were never completed, ending with the completion and commissioning of Project 41, the Neustrashimmy (this is the 1950 one, not the current frigate). There is some good discussion of the political and technical issues and good drawings of some of the projects. I found it a good read. This is available on-line at the wunderwaffe site (Russian Language).
There are some others. I'll see what other options I can give you.
Hope this helps.
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