I suppose the reason why many ebuilds use the redundant econf || die is that the "die"-part is undocumented for econf in the manpage of ebuild(5). Quite the opposite, it is stated there that econf is a "replacement" for configure and performs "${ECONF_SOURCE:-.}/configure ..." I suggest that "|| die" be added there (even if the actual implementation is slightly different).
Thanks, this is in svn r13600.
This is fixed in 2.1.6.13 and 2.2_rc33.