In ONE episode.
Right now there is a HUGE grin on my face. :-)
For those of you who aren't keeping track, that includes the following future Justice Leaguers:
Cyborg (Ok, technically he's not in the Justice League, but still...)
The rumour mill is spinning that there may be a Justice League spinoff. At this point, it's probably just that: rumour. But still... they DID produce an Aquaman TV pilot and Smallville has been extremely successful ratings-wise.
Personally, I just can't imagine that Tom Welling will want to continue in the role after seven years, especially if he's got to wear tights. Also, it would be a very expensive show to produce on a weekly basis. And of course they would have to find a way to bring Batman into the mix, and the producers of Smallville have stated quite clearly that the (young) Dark Knight will NOT be appearing on the show.
It could be pretty cool though...