My group and I did multiversing in the 1980s, 20, 25 years before. It's the inevitable manic logic for long term campaigns, no matter what genre they are set in. Just like it is in every long running superhero comic book.
Back then recall that there were dozens of RPGs for every genre and it wasn't really until Steve Jackson Games came along with Man to Man and Gurps in the mid 80s that started the trend for house rules regardless of the genre. I used Gurps to synthesize all the other dozens of characters from other RPGs and converted them into Gurps and used that to introduce these characters to each other through dimensional travel.
But I was well on my doing that in 1985-86 even as Gurps was coming out.
My buddy Jim however, beat me to the punch with a one time adventure pitting our FASA Star Trek Star Fleet TOS characters vs Star Wars adventure NPCs (pre- West End Games by the way, as discussed here). I took it one step further and sent my long running FASA Star Trek players Craig and Ken for long stretches of time, and at the end, permanently into other dimensions.
Dimensional travel is a staple in comic books, with DC's Earth 1, Earth 2, etc of the late 70s, but it was two stories, one from Marvel Preview 15 and one from DC's Green Lantern that inspired me RPG wise.
The plot mechanism I used was something out of DC Comic's Green Lantern comics from the mid-70s (Green Lantern vol 2, issue 92), during my favourite run with artist Mike Grell.
I must have read it when I was 10 or 11 but I never forgot this issue and it was bubbling in my subconscious until about 6, 7 years later I used it on my players in 1985-86. In this comic, a mysterious device called the Silver Twist appears and whisks Green Lantern, Green Arrow and Sinestro (the traitor Green Lantern) to another dimension "that may not even exist."
I imported the Silver Twist into my FASA Star Trek universe and even had an NPC, the least educated most streetwise NPC in the merchant crew paraphrase Green Lantern by saying "No one knows who built it or why." And then, of course, I had their Star Trek mission-class ship enter another dimension for an adventure through the Twist, the first of many starting around 1985-86.
|FASA Star Trek Mission-class merchant ship|
Years later, the Twist as it we called it, was eventually trusted by the PCs who just went with it. I never did explain the origins of the Twist to the players (as the origins are not explained in GL # 92, or indeed in any issue of GL as far as I know). It was sufficient that it was there, seemed to be omnipotent, and got the PCs to other dimensions whether they wanted to go or not. When I finally finished our TOS Star Trek merchant campaign about 1990-91 or so after 5 years of hard gaming and some bitterness at what TNG was doing to Trek, I sent off our PCs permanently to other dimensions, sailing off into the sunset as it were, with a gift from the Twist.
I thus used dimensional travel extensively, and I'm kinda sore that somehow I missed Richard Tucholka's Fringeworthy in the 1980s. I found the first edition on ebay in the late 1990s, but by then it was far too late for me as I retired from RPGing. But man, if I stumbled upon it in the 1980s, I would have went apeshit with it.
|Original 1984 edition|
What's galling is that one of my first RPGs I ever played, around 1980 or 81, was an obscure RPG called The Morrow Project, also by Tucholka. Not many people heard of it in the early 80s, so I don't know how the hell I missed his ahead-of-it's-time dimensional travel RPG "Fringeworthy" entirely, and I was that one guy in our 7 man RPG group who really really loves the alternate Earth genre.
Anyways, the Silver Twist idea was lovingly used and am glad those adventures are memorable, even after 30 years.
I've documented elsewhere in this blog that I had Star Trek characters play with West End Star Wars characters for over a dozen published WEG adventures in the late 80s, using the Twist to put the former among the latter.
In the early 2000s, I GMed by PBEM a Dimensional Patrol campaign and really enjoyed it, especially when I used pictures and ideas from the TV show Sliders. I took the idea of a "jump belt" from a story in Marvel Preview # 15 called "World's Enough" and had the PbeM PC and NPCs use it to travel from Dimension to Dimension.
My point is, after you play a long time in any genre, and the players get antsy, I think it's inevitable that the GM will send them "elsewhere" just to mix things up. Characters can only expand so far in their universe without upsetting the status quo, of that universe, such as politically. If you don't want to do that, like I didn't for the Star Trek Universe, you send them elsewhere for their own personal character growth.
I did it also for the love of Dimensional Travel and Alternate Earths stories. I just love them and loved GMing that super-genre.