What's amazing is how many companies who buy expensive firewalls for their corporate networks to do this on purpose under the illusion that somehow having LAN computers not being able to access anything besides outbound HTTP and HTTPS on the internet makes you more secure.
Haven't they noticed that everything piggybacks on top of HTTP/HTTPS these days? Even VPNs. You're protecting nothing.
Blocking outbound traffic at layer 3/4 does not require an expensive firewall. It provides protection against certain attack vectors, but as you say, most stuff nowadays uses http/https and in the case of trojans, likely reverse shells. Any firewall should be able to do this.
The expense usually comes in when doing application layer filtering and/or transparent/active proxying, which is the point at which you can block SSL VPN clients and the like. To do this over HTTPS it obviously requires MITMing TLS traffic, which I have mixed feelings about.
While technically true, reason this is the killer feature of IPv6 - by far - is that it removes the need for NAT, restoring the most powerful feature of the internet: being able to publish as an equal peer without requiring the approval of a 3rd party.
Stuck on a "party line", network software was forced to find complicated workarounds[1] and de facto prevented most serious development of entire categories of network software. In practice, you still needed a 3rd party - usually some centralized service - to grant each peer their imprimatur[2].
The power of the internet is that it allowed unrestrained, ad hoc publishing. Entire protocols - such as HTTP - could be developed without first getting the approval of some governing body. We have done a very good job of pretending we still have this capability, IPv4 went the way of cable TV a long time ago.
Why is it taking so long to deploy IPv6? That's easy: a conflict of interest. Why would a big company that controls a scarce resource - IPv4 addresses and the publishing power the represent - want to dilute their power by with IPv6? These companies were based on refining Shannon's ideas bringing the cost of coping data rapidly to zero. They saw what happened when groups like the {RI,MP}AA became obsolete. Why would they want to invest significant amounts of money in their own obsolescence?
APPENDIX:
Whenever this topic is brought up, someone inevitably cries that that NAT is necessary "for security". This misconception happens when NAT/"IP Masquerading" and a statefull firewall are conflated. You can drop packets without changing any addresses (firewall only), and you can rewrite addresses without doing any packet filtering (NAT only). While these features are often used at the same time - especially in cheap home routers - they can be (and are) used independently. A firewall should still be used with IPv6.
Occasionally this "for security" concern is a concern for privacy. The NAT "party line" is seen as a source of anonymity ("you don't know which machine behind the NAT is making a request. First - how many bits of anonymity are you gaining in practice? Second - if HTTP is involved, the browser is probably leaking addresses anyway (WebRTC[3]). Finally, is your source port or TCP timestamp[4] leaking information?
[1] http://www.brynosaurus.com/pub/net/p2pnat/
[2] https://www.fourmilab.ch/documents/digital-imprimatur/
[3] https://bugzilla.mozilla.org/show_bug.cgi?id=959893
[4] 0x03-2 http://phrack.org/issues/63/3.html
edit: grammar