Yes, heck its part of the theme of the realms from the beginning, Mulhorand was influenced by Conan, and I guess by extension Thay. Stygia to be specific. It ate the Moonshaes. It ate Kara-Tur from Oriental Adventures, Mazeteca, Al-Qadim. It connected to both the Nentir Vale and Athlas (Darksun) via the the Abyssal Plague books. I don't remember the older series, but there was a trilogy that connected the realms to Dragonlance and Planescape. Heck it even built another world for the purpose of eating, Abier. The Gloomwrought book was originally for the Nentir Vale setting, but it ate that too. Evermeet ate Spelljammers. There are domains in Ravenloft from the realms and now that the domains of dread are a default part of the Shadowfell, it ate Ravenloft in turn.
Heck its not even limited to D&D products. Kalamar's gods have a pact with the gods of FR to grant each others followers spells when they are in the other gods world. Sharess and the Vicelord for example aside from having very different moral positions have a deal to support the worshippers of the other other god.
Realms comics at one point I believe where written by DC comics, which connects it to the DC universe, which at one time was connected and united with the marvel universe, and marvel had a novel called Planet X that was a crossover between Star Trek and the Marvel Universe.
Mystara and Birthright should be afraid, the realms is still hunger, and they look so tasty, and protected. And Starwars and Stargate, well those would make a nice nearby galaxies that could be connected to the realms via Imaskari Portals, and the Wheel of Time world, well the Shadowfell could no doubt have a path straight to the darkones prison, sure it makes little sense and copyright and all that, but the realms is hungery and won't be denied. Actually there was that World of Darkness D&D book wasn't there and Ravenloft was published by White Wolf for a time. And the New World of Darkness and the Old World of Darkness has some connections I believe.
The realms is hungry and coming for an IP/Setting near you.
Mawahahahahahahahahaha. Resistance is futile in deed.