IPv6 gets rid of NAT, which has certainly been a large part of avoiding accidental exposure of services to the internet from internal hosts.. so in that way, yes, it's a change to how most everyone is doing things.
However, it doesn't at all mean that you won't still have a central firewall at the network edge - the change is simply that it'll be acting as a pure firewall instead of a firewall/NAT device. It'll just be up to the people managing those firewalls to make sure to avoid accidentally exposure of services; fire up the deny rules!
Getting rid of NAT is a big change to network security practices, and there will certainly be times before too long that we hear about some accidental information exposure breaches due to misconfigured firewalls and IPv6. But NAT has always been a hack, and getting the firewalls out of the business of tracking all of those connections and fake connections for stateless protocols and port translations will be a good thing in the long run - less complexity sounds good to me!