Bitcoin is dead as we know it if you raise the block size.
Okay, that is definitely a bit hyperbolic to say the least. If the quadratic validation time get fixed (which should happen with Segwit) I can see a future in which a block size increase is definitely possible. Just today we've 'received' two amazing news: Fibre (upgrade to the relay network that builds on compact blocks) and Flare (Bitfury's LN implementation). With the proper infrastructure in place, I do not see a reason for which a HF on which consensus has been reached (with a proper set of rules) should not happen sometime in the future.
The node count as we have it now is low already at around 5000. If you double this, you can expect a lot of the widespread % to decrease. Even if the total node count went up, the system would be more centralized if specialized services for running nodes arise.
It is really unfortunate that, with so many people running around on Reddit and BTCT that we are unable to keep a higher node count. If half of us were to run a single node, the situation would definitely improve.