Hey this thread from my old account is still up! Anyway I still stand by what I said, both Inuyasha and Fruits Basket (manga/2019 anime) are two very good anime that would fit well with Sailor Moon in a crossover.
1. Inuyasha: 90's anime wise mostly, because you could easily headcanon the BMC as being the last remnants of hanyou dating back from the Sengoku era and that's why the Neo Queen and King forced them to either be cleansed or banished. (Personally for me I headcanon Prince Demande is half ogre demon, hence the 3rd eye) I've also read old fandom fics that wrote Demande & Saphir's relationship alot like InuKag. (Which got me to start shipping them in the first place seeing as how InuKag is my number 1 canon het OTP of all time) The two series also share similar themes such as Reincarnation, Time-Travel and Crystals, plus with Rei being a Miko and looking very similar to Kagome (and them both even being archers!) you could easily headcanon them as being related.
2. Fruits Basket: I don't wanna give out spoilers, but in a previous thread I made I cited this series as being possibly influenced from Sailor Moon, the reason being one of it's couples eerily resembles the Usagi/Mamoru relationship. The man in the couple feels he's destined for his lover because he saw her in a prophecy dream (sound familiar?) what makes this so easy to crossover is that this prophecy dream and why he felt so attached to it is never explained so you could easily make a crossover where this couple are AU reincarnations of Endymion/Serenity (I actually wrote a little one-shot for a FB zine based on this crossover) The main villain of this series is also eerily similar to Beryl, and the man I mentioned even grew up together with 4 other boys who could easily fit the roles of the reincarnated Shittenou (two of them who are especially close even have extremely similar personalities to Zoicite and Kunzite in fact!)
Some other series that I feel would be a good fit:
3. Madoka Magica: I am fully convinced this franchise was wholly influenced by the manga arc of Stars as it explores very similar themes and Chaos could easily be taken as the equivalent of Entropy, plus Madoka and Homura's dynamic is very similar to Chibi-Usa's and Hotaru's. An interesting crossover idea exploring this could have the Cats actually be variants of Kyubey and the whole past Silver Millenium and future Crystal Tokyo they showed the girls were actually all lies and illusions in order to make them "Senshi." (i.e. Meguca).
4. DBZ: I mean, it's one of the most popular crossovers with SM for a reason. It's SM's Shonen equivalent, plus both series deal with space and aliens/ailen civilizations so I feel Saiyans and their history could easily fit within the Sailor Moon universe.
5. Ranma: Again, another commonly crossed over series that's popular for a reason. I personally like to also headcanon Demande & Saphir as the reincarnations of Ranma and Akane.
6. Final Fantasy VII: What if Aerith was actually the Senshi of Gaia and Jenova was an incarnation of Chaos?
7. One of the Tales games, maybe? Don't ask me why but I feel like Tales of Legendia in particular would be a good fit (only for the 90's anime though) as it's a game that follows the story of an oppressed indigenous civilization that turn extremist due to that oppression, I feel like the Ferines and the Black Moon Clan would be able to understand each other in that respect, plus both groups features a younger sibling that has unrequited love for their older. (Though in Tales of Legendia's case, the siblings are definitely adoptive)
8. Yu-Yu Hakusho and/or Hunter x Hunter: I mean they're both made by Naokos' husband, shouldn't a crossover be inevitable?
9. Precure: Instead of Precure's obligatory within-universe crossovers it'd be cool if they did a special crossover episode with Sailor Moon, I mean they're both Toei franchises and are the biggest Magical Girl franchises of their respective generations, Sailor Moon was also Precure's influencer so a crossover episode would be a nice homage.
10. Kingdom Hearts: This is THE Crossover series, how could I not include it? Anyway, even though it's mostly Disney based there should be a Sailor Moon world Sora & Co travel to.
11. Utena: Both Ikuhara directed series, and it'd be cool if Utena & Anthy were parallel/AU versions of Haruka and Michiru. Both the characters and relationship dynamic is very similar.
12. For a non-anime/non-Japanese based option I actually think Steven Universe could work pretty well? Rebecca Sugar has already made it known she's a big Sailor Moon fan and SU was clearly influenced by it, but honestly just the fact that it's again another series based around Space and Alien Civilizations it'd be cool if the Gems civiliazation had their own place within the Silver Millenium, or if Rose and Steven himself are the Senshi of their respective planets.