I can’t really do this for English fandom, because aside from mine, there are only about 3 other fics in the fandom which I know of. Russian fandom, however, has been a bit more productive. I kind of have always liked to speculate what sort of parings, characters, tropes, etc would be popular in War and Peace fandom if it was large like, say, HP, Sherlock or OUaT or Merlin (or even Downton Abbey). So I decided to do a bit of a parings census from some sites which hold an organized majority of easily accessible fic in this fandom. Notably, while one of the authors particularly has been more prolific than others - which tends to skew numbers a lot more overall in tiny fandoms than large ones - the majority of fic is written by a variety of authors, which is good for representation purposes.
Caveats:
-It is not unlikely that an active English fandom would look different. Russian fandom and English fandom have their differences.
-This is just a quick count of parings. Genfic was no counted. Individual characters may have a different rate of representation.
-I generally counted the parings with which fics were tagged, however there was some arbitrary judgment on what was a prominent supporting paring (which were included) and which was just a minor background/mention only paring (which were not). The couple of times this happened these were mentions of canonical marriages which were not very important to the overall romance part of the fic. But, yes, there is a bit of a judgment call there. (I’ve read…just about all of these fics, so the judgment call wasn’t totally arbitrary, fwiw.)
-I did not count “pure” RPF fic (eg; Napoleon/Alexander I) but did count mixed ships (eg: Nikolai Rostov/Alexander I).
-This is only a count for fanfic, not fanart or any other sort of fanwork.
-I did not count my own fics.
-I used fics located on FicBook, AO3 and the diary.ru Russian Classic comm by searching the War and Peace tag (fills for the comm fest(s) included). This was done for “fairness” purposes as well as ease for me. I know of the existence of some other fic, but my knowledge may very well be skewed in favor of parings/types of parings (eg: slash) that I like because I search them out specifically and rather meticulously. These archives, on the other hand, are easily and equally accessible to anyone in the fandom. (For anyone who is interested, I am aware of an additional 2 Dolokhov/Anatole fics, 1 Dolokhov/Sonya fic, and 1 Nikolai/Alexander I fic which were not included in the count).
That’s a lot of caveats, but hey, this is just for fun :)
Summary:
Unique parings: 21
Slash parings: 11 (used 30 times)
Het parings: 8 (used 18 times)
Fem parings: 2 (used 2 times)
The most popular paring, by a fairly large margin, was Dolokhov/Anatole (11 fics) which is fun for me, seeing as they’re my OTP :)
Second place with 4 each is divided between Andrei/Natasha, Nikolai/Sonya and Pierre/Andrei.
Third place, with 3 fics each was is shared by Anatole/Natasha and Dolokhov/Petya Rostov.
Dolokhov/Anatole
11
Andrei/Natasha
4
Nikolai/Sonya
4
Pierre/Andrei
4
Anatole/Natahsa
3
Dolokhov/Petya Rostov
3
Andrei/Anatole
2
Denisov/Petya Rostov
2
Dolokhov/Nikolai
2
Dolokhov/Sonya
2
Nikolai/Alexander I
2
Nikolai/Maria
2
Denisov/Vincent Bosse
1
Dolokhov/Helene
1
Dolokhov/his sister
1
Helene/Natasha
1
Nikolai/Ilyin
1
Nikolai/Nikolai Bolkonski (Jr.)
1
Petya Rostov/Vincent Bosse
1
Pierre/Natasha
1
Sonya/Natasha
1