Dunno if there's a limit on how many survivors can be held at the same time, but if there's no problem, I'd start the Meta-StevenWilson survivor this weekend
I mean, I don't know anything about any imposed limit, but here's what I think:
The past couple of months there have really been four going on: Nightwish, Neal Morse, Devin Townsend and Periphery. Periphery and Devin Townsend I believe just ended. Nightwish is going into finals within the week. Neal Morse, I believe, is on the final album. Essentially, all the survivors that have been running the past few months have either just ended or are approaching their end.
DT the League is about to start up, which is a lot of Polls/Survivors traffic. IDontNotDoThings is starting King Crimson. Sacul is starting Steven Wilson. The Letter M will replace Neal Morse with Spock's Beard once that finishes. Evermind will do the same with Kamelot replacing Nightwish (with Beyond the Bridge possibly intervening). Elite is starting Haken soon. So both the currently ongoing survivors are going to be followed by additional survivors by the same organizer, while a few organizers who have not been running survivors are about to start them up.
We can look at these as slots that are being filled. Here's what we have:
Nightwish (almost finals) ---> Beyond the Bridge/Kamelot (same organizer)
Neal Morse (almost consolations) ---> Spock's Beard (same organizer)
Devin Townsend (finished) ---> King Crimson (different organizer)
Periphery (finished) ---> Haken (different organizer)
[EMPTY] ---> Steven Wilson
So, with all this transition going on, we're basically going from 4 survivors to 5 survivors plus DT the League. Plus, Train of Naught is toying with the idea of Avenged Sevenfold and I'm toying with the idea of Iron Maiden.
Personally, I think 7 survivors plus DT the League would be a bit much, while 5 plus DT the League is a good amount. I don't know what anyone else thinks about this, really, so I might be totally in the minority. But personally I think 7+DTtL would be a bit overwhelming.
With that in mind, I'm probably going to hold off on starting Iron Maiden until something finishes. Maybe after Elite's Haken survivor is over, since that one won't be a super-long one anyway as there are just three albums and an EP. I'm not trying to tell anyone else (Sacul, Train of Naught) what to do or not do, I just don't want to personally be the one to flood the Poll/Survivors forum.