Toady talks about it in some of the DF talks. Basically, there's 3 groups of players:
-Simulationists: Want to have the game as "realistic" as possible
-Game-ists: Put gameplay above realism
-Builders: Those who come up with the giant marvellous megaprojects.
It's hard to strike a balance, but I don't think this will really "benefit" any of these groups.
It won't benefit "any" of them, it would benefit ALL of them. Easter eggs in indy games are a way that indy games create links to each other that players can follow. Indy games certainly benefit from this, but DF does not participate in it that I'm aware of. I do not believe that diggles in the game will have any impact on DF itself, provided that they don't bring in silly abilities that no other creatures have. However if Toady chooses to be hypersensitive to intellectual property even if he's given permission to easter egg another game, that's HIS choice to make. I will say that DF and Toady have a GREAT deal of respect in the indy games community. The chances of an indy developer giving Toady any sort of a hard time about usage rights if Toady gets permission from them to use something of theirs in an agreed-upon manner as an Easter egg is not even quantifiable - the indy community would shut that noise down so fast it wouldn't even be funny - and the indy devs out there know it.
If actually adding a creature to the game that comes from another game is something that Toady simply doesn't want to do, there are a couple fairly other simple (seeming) options that would serve as Easter eggs as well.
Maybe plant diggles and other possible future references into the decoration system so dwarves can create artifacts and engravings with images of diggles on them, even if they never appear in the game as creatures. Perhaps allow them to appear occasionally in the world history but never in the actual game. Finally, they might be added to the database that dwarven preferences for animals, allowing us to have dwarves who like diggles for their amazing nasal appliances.
Easter egging need not impact primary gameplay at all.
*shrug*
I'm done here and will just bring up this thread with my next donation to make sure Toady considers it, rather than asking for a crayon drawing. Or maybe I'll ask for a crayon drawing of a diggle, lol.