Actually, NexusMods does have a fully fledged installer that works for most of the 1k games they support. Vortex is a fully supported installer that not only helps manage hundreds of mods for each game they support, but also allows for multiple mod profiles for the game, archiving, etc.
Someone mentioned partnering with Nexus Mods and that is very difficult. When I was responsible for the UGO dot com’s old Games Network (prior to Hearst then IGN acquiring the domain) we and many other ad network sites (e.g. Crave, IGN, ZiffDavis) tried to seduce Nexus Mods and get them to become a partner. The founder is extremely business savvy and asks for a lot for Nexus to be involved in anything - as he should given that site over the past 16 years has become “the” destination for quality mod content. Given the pedigree of Julian he may have better chances than a group of ad networks hoping to ad Nexus to boost their sellable ad inventory.