There's not an Iron package for VL yet. Previous versions have been fairly stable, but the latest current seems to have problems, so now's not a good time to package it.
Midori is kind of a "tweener" as far as features vs. resources goes, but we don't have the right WebKit package for it right now. WebKit's a tough build; I have an interest in seeing Midori come back, but with all that's going on I don't think anyone has time to handle a basically brand-new webkitgtk or webkit2gtk build right now.
Part of the interest in using Chrome code is probably Flash. The vendor (and why don't we just let them rot) is only doing real "linux" updates for Chrome's interface.
Thanks roarde, very informative - I appreciate the detail of your post.