Basically, default effects.
When it comes to not including Eladrin in your game, I really think these are minimal.
Sounds a lot like halflings are a nuclear option in your games
Not remotely. If someone wanted to play a halfling that would be their prerogative. I just don't care for them, mostly on grounds that they're rather silly outside the very narrow LotR context, and so I don't use them.
Though this exchange has reminded that one of the players in my current game was planning, at the start of the campaign, to play a halfling fey warlock called Peter. But in the end he went for Wolfren, the half-elf fey warlock (who died at 3rd level and was replaced by Jett, the drow chaos sorcerer). In anticipation of Peter, I placed a halfling slinger in the first encounter for the campaign. I thought he could be Peter's nemesis. When Peter didn't show up, the slinger's moment in the sun never came.
Halflings have been shown to add long-term fun to a lot of tables (they've been in the game and reasonably well-liked by the players since OD&D), so for the designers, you'd probably want to consider keeping them in, even if some players hate 'em. It's clearly not much of a deal-breaker for current players, and a lot of people have fun with 'em! But elfladrin were a gamble at 4e's launch: maybe they'd pan out, maybe not. And by removing other options to make room for eladrin, they were telling players who wanted to play the game supported by WotC that these eladrin should add more long-term fun to your table than the options they removed.
<snip>
4e told you how you should play guitar.
I think this is all a bit exaggerated. By putting in eladrin rather than (say) half-orcs they're not
telling anyone anything. No
instruction is being given. It's in the nature of an offer, or a suggestion - "Hey, here's this thing we think you might like!"
Any change has this sort of character - it is an offer of something new in lieu of something old. It's not an instruction to adopt or like the change. This is why I don't agree with the language of "forcing" or "need". If the desire to play with the latest canon was an addiction in the literal sense, then perhaps that sort of imperative language would be apposite. But it is not. If people simultaneously
want to play the latest canon but
don't like the latest canon, that is a commercial problem for WotC (because their potential customers will be unhappy and distressed) but it is not a case of WotC having
told anyone how to play, or having
told anyone what is fun.
PF was a lot more open to whatever you wanted to bring to its hippie drum circle. You could play whatever kind of elf you wanted to in either one, but only one was going to tell you that you were doing it wrong if you didn't do it their way. The other one passed you the OGL and told you to have a good time.
I think this is also exaggerated. No one needs the OGL, or any sort of legal permission, to change things for his/her home game. Anyone who wanted to play 4e but without eladrin was free to just ignore them (or to use them as celestials - a trivial house rule) and to just use elves, or allow elves with a bonus to INT instead of WIS.
There was no OGL in the first 25 years of D&D's existence, but people ignored or changed those parts of the published books that didn't suit them. I don't think I was exercising some sort of superhuman power in ignoring the halflings in all of ICE's Rolemaster books, or in converting the default Rolemaster elf stats (Tolkien-derived) to fit better with my conception of Greyhawk's (D&D-derived) elves. In my 4e game, I've ignored some errata, and applied errata (and other changes) of my own, without worrying about a lack of official authorisation from WotC.
The switch from LE to CE happened in 3e.
<snip>
Your example is minor. Tiny. You can ignore it by ignoring two small letters. It doesn't affect the portrayal of orcs in the past, change much of the lore, or affect your world.
You're correct that it happened in 3E. That was a typo in my post.
I don't agree that the example is minor. If you treat alignment as a personality/society descriptor, it is not tiny at all. It is a major change in the personality and social character of orcs.
The only way that it doesn't affect my world is if I ignore it.
But anyone is free to ignore 4e's changes to the eladrin, too. Or to strike out "fey" in the Monster Manual description and insert "immortal". (That's one word to change, not two!)
Turns out, they were right in some places, and wrong in others. And they were wrong, perhaps predictably, in regards to a lot of "hardcore" D&D players, who left for PF or the OSR. And where they went, people down the pyramid followed, because network effects.
Do we have any polling or survey data that tells us how many players left D&D for PF because of eladrin? Frankly, the idea that such numbers were significant is a conjecture that I find pretty implausible.
After fairly extensive market research, WotC has decided to include eladrins as a PC race in a 5e core book. I'm therefore guessing that they think they were right to suggest that people might find eladrin fun - that they think that plenty of people did like them.
Much as Gygax and Arneson were right to think that many people might want playable hobbits. But they weren't telling us that we
had to play hobbits if we didn't want to.