In a word no. Enjoying something simultaneously doesn’t mean the same as inspired by. If Terry Pratchett watches the Star Wars films and enjoys them, it doesn’t mean he was inspired by Star Wars.
I’ve seen the Forum reference you provided to the origin of Pratchett luggage being a d&d game. The dedication for his novel Sourcery reads...
“Many years ago I saw, in Bath, a very large American lady towing a huge tartan suitcase very fast on little rattly wheels which caught in the pavement cracks and generally gave it a life of its own. At that moment the Luggage was born. Many thanks to that lady and everyone else in places like Power Cable, Neb., who don't get nearly enough encouragement.”
Now did D&D inspire the luggage... or did Terry Pratchetts idea for the luggage make it into one of his D&D games? D&D fans love to think that D&D creates the work of writers they like but I’m a bit more sceptical.
Regarding D&D swelling the market. The actual numbers of people playing D&D was still relatively small in the 80’s, and arguable the 90’s and 2000’s too. Considering total turnover ranged from 2m to just shy of 9m over that decade. I’ve seen figures from 2007 suggesting the various editions PHBs sold between 0.7m and 1.5m. Only an indication but a useful one.
The colour of magic alone has sold 20 million copies. I’m not sure there is any evidence that the people who bought and enjoyed colour of magic did so because they played d&d rather than just being a fan of fantasy fiction.
A quibble: The Colour of Magic sold 20 million copies since it was published in 1983 - nearly 40 years ago. Whereas the 2-9 million number for D&D players (which I'm guessing is more an estimate, based on the huge range) was just a snapshot in the 1980s. Not really a fair comparison; you would need sales of Colour of Magic from just the 1970s-1980s.
And I'll reiterate, just because Pratchett didn't slavishly copy D&D elements into his novels doesn't mean that D&D wasn't an influence, both on things he put into his work, and on the fantasy literature market that gave his novels a chance.
Now, that said, Pratchett's
first fantasy novel was actually published in 1971, and it's clearly a Discworld precursor. So many of his ideas are clearly not owed to D&D. On the other hand, said first novel didn't make a big impact, and it was five more years before his next novel, and 12 more years before he ventured into fantasy again. And D&D popped up in the middle of that span.
To be clear, I'm not trying to suggest that Pratchett was some hack who wouldn't amount to anything without D&D. That would be silly. The point I'm trying to make is, you need to be very picky about what fantasy influences there might have been on D&D in this alternate timeline. It really should only be ones that are far removed from D&D and its tropes, the sorts that could stand alone without any impact from D&D. Anything that could have owed something to D&D is at risk of either not existing, or looking rather different.
Another thought for magic might be to go closer to medieval Alchemy, where it's a combination of hot/cold/moist/dry. Possibly mixed with elements from other cultures, like Asian elements which included wood and metal, or dismissed scientific elements like ether or phlogiston.
Yeah, alchemy and elemental magic certainly seem likely as sorts of magic in this alt-D&D. I also stand by my earlier assertion that psionics/telepathy/etc. would have a prominent role, since the first RPGs would likely bring in SF tropes.
You're probably right at least partially there. Baseball cards were always a thing, but they were more about collecting, so the Mons genre (or something akin to that) would also be heavily collectable. OTOH, according to Wikipedia fantasy golf was invented in the 50s, and fantasy football in the 60s. So it's just possible that CCGs would eventually evolve out of that. It just needs someone who was both into fantasy sports and collectable monsters and/or magical battles. I doubt it would happen in the 80s or 90s due to the jock/geek divide, but nowadays, sure.
Oh, I do think CCGs are still possible. As noted, Richard Garfield would still have Cosmic Encounter as a possible inspiration for the CCG. (Though there is the question of where they'd market such a game, as CCGs initially relied on the D&D/RPG community for their early spread.) Whether we get a Pokémon CCG, harder to say, as there are a number of complications (what's the CCG market like in 1996 Japan in this timeline? is Wizards of the Coast big enough to market the CCG in the west? is there a market for a monster-collecting CCG in the same way there is a monster battling game?).
Or if not fantasy sports, maybe chess? One of my favorite computer games in my Commodore 64-spent youth was Archon, which was basically fantasy chess with monster battles. If you haven't seen it, then what happened is that you couldn't just claim a space by landing on it like in real chess. Instead, you had to battle the piece that was already there, and your strength, speed, and attack powered varied based on the in-game moon phase (full moon/light pieces; new moon/dark pieces). It was almost certainly based on D&D, going by the monsters involved (manticores, golems, unicorns, basilisks, etc.) but chess is a possible precedent.
Not to get off-topic, but I played the similar Battle Chess back in the day. (Though I've also played the NES version of Archon. I like it but it kicks my butt.)
In any case, we haven't even seen a chess-based RPG in our history (that I'm aware of), so I dunno if it would be an influence on this alt-D&D. (Though now I'd like to see someone try making an RPG like that...)
EDIT: Wait, were you suggesting chess, or chess games, could have inspired monster battles in Pokémon? I suppose it's possible, but despite Archon and Battle Chess being a thing, neither seemed to be massively influential in the way that D&D-style RPGs (and later, JRPGs) were on the Japanese video game industry. But who knows, maybe it was D&D-style RPGs that kept such mechanics from getting a shot.
