Better support for old version(s)
I understand you guys want to move fast in order to release more and more awesome features, but for a lot of people using a shopping cart has only one goal - make money continuously.
1.6.x and 2.0 are non compatible releases when people have customized plugins and themes on top of the existing WC code base - even the upgrade is fully automatic. Critical issues like this  and critical security updates should be applied to both versions and keep parallel running for a certain period of time.
I understand the resources are not infinite, one of the solutions I can think of is to release an "enterprise version" like rubylts  so you can charge like those existing premium modules.
Yes. Wordpress currently releases security fixes to the 4 last major versions, e.g. current release is 4.0 but the last security release was rolled out for 3.9, 3,8 and 3.7 too.
I would not ask for the same for WooCommerce, but the previous release should also get security updates, e.g. current version is 2.3 but 2.2 should also get security related fixes.
Shop owners love stability. This includes not being forced to do major updates every 6 months (which means overall testing of all shop features including theme, plugin, payment gateways and see if local (code/css) customizations still work).
For me, one major shop update every year would be sufficient. Currently, this is not possible with WooCommerce's release policy resulting in high maintainability and administration costs.