Plus most Linux users have always used or are always using the command line. I believe a simple step by step "howto" guide should be easy to follow for anyone who uses Linux.
I believe that the majority of people running Linux nodes are split into two groups:
1) Those less familiar with it and/or running GUI - use PPA.
2) Those that are quite familiar with it, and manually download binaries (and/or build them).
In either case, I don't see OP's statement to be in line with reality. This is especially the case with PPA where you basically only need to run 'apt-get update && apt-get upgrade' and everything is done.
I was about to ask about that. Would it have been better, in this instance, if the alert system was still at the developers' disposal?
Actually it wouldn't. AFAIK the way that the alert system was implemented was also problematic; there was no sure way to tell how many people have access to the key(s). So for example, if an agency compromised a single developer and took the key we couldn't really know (heck, he might not know himself if they did it secretly while they question him on some false grounds). Additionally, it is an issue of centralization vs. decentralization again which is also why it eventually got thrown out.
But is that enough? There is about 80% of nodes that have'nt done the upgrade.
~70%. Use this:
https://bitnodes.earn.com/nodes/ for a sufficient estimate. The thread isn't as serious as it was assuming miners and major economic players have updated, and given that a large portion of the network already did upgrade. I'm certain that the release of 0.17.0 will speed this up as well.