The sex mods will surely upgrade the romanceable stuff, I can bet on that. The Oblivion, Fo3 and Skyrim had proably the most moddable in-game sex ever, though buggy as hell and with laughable animations because scripters can't into animation.
Skyrim has a certain.. mod framework which enables you to use animations by.. err.. animators.
Also, a certain romance mod makes use of said framework and does so quite well.
However it is still an.. erm.. questionable.. mod.
So if you are easily offended by porn or other content related to sex, it is probably not a mod you would like.
However the modder who made the romance mod, have made a SFW version which is on the Skyrim Nexus.
You're proably speaking of FNIS. It's not only a "certain romance mod" from Nexus but whole bunch (like, shitton, a lot of them in varied stages of WIP) mods on certain site (the people behind it made a visual sex mod even for Morrowind, which is SOMETHING), most of them are heavily centered on "not-exactly-vanilla" sex. The Oblivion mods are even more... extensive due to game being around for much longer and the F:NV (F3 got barely any support, for some reason) also had a lot of it, even more "not-exactly-vanilla" due to stuff like NCRCF and Legion way of treating women. And there is even more of this stuff if you're willing to dive into Japanese internets.
Don't ask me where I got this extensive knowledge.
EDIT:
Also, yeah, they started working on FO4 even before the game got relased (making meshes of less-than-revealing outfits and stuff, planning the whole thing and stuff, making art and basically doing a circlejerk (quite literally)) and while now they are busy playing the vanilla game waiting for F4SE, it's safe to asume we're going to get a lot of it soon.