One consistency over the decades of gaming that I've enjoyed has been the presence of "generic" RPGs.....those game systems designed to let GMs who want to do their own thing have the tools and means to do so. It seems like many of these games have survived, at least in terms of their overall historical impact on the hobby, over the long decades....even if the systems themselves may languish in strange states of indeterminacy.
Take GURPS, for example: it's still technically in print and available in PDF over at www.sjgames.com and they even have an Amazon print-on-demand option for an ever-increasing variety of books. Sounds good, right? The only real issue is that new books appear to be a thing of the past now that GURPS Dungeon Fantasy has released and it turns out SJGames essentially lost money on it, and cut back inventory due to the fact that the demand for the game outside of the immediate Kickstarter was just not enough to warrant it.
So if you are a fan of GURPS, it looks like you'll have to rely on the existing tomes and a smattering of periodic PDF released. The good news is, being a GURPS fan means enjoying a system on its merits, not it's visibility to the hobby at large. With GURPS, you either "get it" and support the game as it is presented; or, you don't realize it still exists (or have never heard of it to begin with)....there's little in the space between for this game's presence in the hobby.
Chaosium has a similar scenario with BRP. Basic Roleplaying's Big Gold Book (BGB) was a welcome tome for fans of the D100 system, providing a compendium of rules all in one place with lots of customization within the design scope of the BRP system. After Chaosium's return to it's older masters, however, BRP essentially went the way of the dodo. It still has print copies available on Chaosium's website and exists in PDF, but no new BRP projects are in the works, and suggested future plans depend on a variety of slow moving factors: the release date of the new Runequest, which returns the game to the pre-1983 era of Runequest as an exclusive vehicle for the Glorantha setting, with some vague promises of a small booklet with BRP rules that ties in to future non-Glorantha works in the future. Ironically this is all happening in the wake of Call of Cthulhu 7th edition, which handily revamped the rules in a different direction that many people (myself included) really liked. So the future of BRP is very much a mystery....and its utility as a resource for a genric system to design your universe for remains firmly with the evergreen book that has essentially been put out to pasture.
Then there's Hero System. I've never been as enchanted with Hero System so I don't keep up with it's status as much, so what I know on this one depends more on its external visibility to a non-follower o of the game. It appears to have made 6th edition its evergeen product, which is now available in PODF at www.rpgnow.com and other OneBookShelf sites. The website at www.herogames.com appears to show a lively community for the game is out there, with some active projects and kickstarters going. I'm kind of envious....I wish I liked the system better, it seems to have a core base keeping it nice and alive.
Finally there's Savage Worlds. Savage Worlds is alive and well, with lots of IP adaptations of indie comics and genres, and a current project Kickstarter going for Flash Gordon. It even looks like the new Flash Gordon game will upgrade the system mechanically (I think this has already transpired but I cant quite bring myself to get the PDF; I just don't care that much about Flash Gordon!)
Savage Worlds is distinct from the prior mentioned systems in that it operates on a simpler mechanical scale, with an emphasis on quick combat, easy record keeping, and a lower overall resolution of detail (such as 17 skills vs. --say-- GURPS' 700 skills). This can be a huge overall advantage because it is one of the only generic systems where pick up and play games are completely feasible. It is a disadvantage is you want harder granularity and more nuanced mechanical effects in play.
There are a few other "generic" systems out there, but I'm mainly looking at all-in-one books that do the job. FATE Core could count, but it's just a bit too off in its own special universe of design for me to absorb. Powered by the Apocalypse games all have a similarity, but it varies from game to game, and neither of these systems are designed for the prolonged use, delicate prodding and poking and meticulous verisimilitude that the aforementioned systems all offer.
So the question is.....are generic systems on the out? The most recent examples (FATE and PbtA) are aimed at shorter, controlled experiences with little mechanical nuance. Savage Worlds thrives by being mechanically robust, but just enough to provide for a structured environment, but not so much that the rules get in the way of preparation time. By the time you are looking at BRP, Hero and GURPS you are also looking at games that expect you to sit down and work on the planned scenario or world for a bit before proceeding. Sure, each has their "quick entry point," but those are just a quick way of stripping the system down to allow for an easier teaching experience to new players. This has probably not helped make these systems easily adapted by newer generations of gamers, even as their overall reputation and continued support by the older, dedicated fanbase continues.
I feel like there's probably room in today's market for a really good "mid range" difficulty game system to pop up and take the market by storm. Imagine a GURPS which didn't require the sensibility of an engineer to fully appreciate, or a Savage Worlds which allowed for more nuanced skills and mechanics but without ramped-up complexity. Imagine a "generic" version of the core design conceits of D&D 5th edition, but designed with a generic, multi-genre system in mind.
(EDIT: There's Genesys, by the way, a brand new entry into Generic Systems. It's main issue right now is that the core rules don't appear to provide enough toolkit support "out of the box" to make it very useful just yet. I'm not sure I agree with that sentiment, because the game mechanics in Genesys are a special breed....it's not how it runs, but how you reskin it, essentially.....but the Realms of Terrinoth sourcebook is out soon, and will probably settle for many just what Genesys's potential is when it's not the stripped down engine for Star Wars).