Not likely to often be an issue, but I'd rather be specific.
I am in agreement. Playing a character from another show in a related franchise feels very much "recurring" appearance.
If people are opposed to the proposal, I'd personally like to hear from them. Just because this information doesn't seem at all spoilery to me, it might to others.
Apart from the Rainbow of CSIs, that's all I can come up with.
I am tempted to suggest on the same grounds that a guest appearance by Richard Belzer be automatically considered a spoiler, no matter what the show.
I can think of situations where one might make "reasonable surmises" based on knowledge of the season, if an actor were high-profile enough (Let's say "Nimoy's going to be in the Season 1 Fringe Finale? With a name that big, I bet he's playing William Bell.") But that's the kind of situation that's likely to be kept under wraps or to be in promos.
The Belzer exception is making me laugh.
I am tempted to suggest on the same grounds that a guest appearance by Richard Belzer be automatically considered a spoiler, no matter what the show.
This is also reasonable. And funny.
If Pauley Perette is going to be on NCIS: LA, it's a fair bet Abby is showing up.
Just for example of franchises.
I'm fairly spoiler-averse, but this seems entirely reasonable to me, especially with the franchise restriction.
I would restrict it by "existing character" or similar, not franchises -- that gets Munch in.
"The Belzer Exception" would be a pretty good name for a band.
Also, I support this proposal.