SG6 not coming is a problem. Sure, MCSG will still be gaining lots of community maps...but let's be honest here, who has the bigger youtube channel to showcase these maps? :/
Vareide has a big channel, and a lot of the userbase has come from when he made these videos and linked MCSG at the end. A lot of users came here for the new maps...but who's going to come when it's exclusive to another server?
I can see SG6 taking quite a hit on MCSG - The userbase is already slightly declining from the loss of Bajan and his Bacca's, and there will always be the large number of users leaving due to it not being like the "1.2.5" days...this is all not to mention the loss of staff members recently from the many resignations. Another hit from SG6 is the last thing MCSG needs; MCSG could really use the influx of users that come during SG6's release right now.
I really hope MCSGv2, when it's fully complete and bug free, is as amazing as it sounded. MCSG could really stand to be stable and amazing right now, something that will make users tell their friends this place is amazing. Right now, admittedly, it kind of lacks...achievements, a complete leaderboards page with weekly/daily stuff, general stability, etc...a lot of things it was supposed to have months ago.