Notice in the iFixIt teardown ... the SSD socket is not included on the motherboard on HD only models!
No opportunity to add a SSD later if desired ... even if you are willing to cut the adhesive tape holding it all together.
Looks like only the entry 21.5' model doesn't include SSD connector, check out http://www.kodawarisan.com/k2012_02/archives/2012/11/aa_imac_aeaaa.html which is higher model.
And I think all 27' model will have it.
Though since the panel is glued, maybe just order the Fusion Drive...
I'm fine with the removal of optical drive. But other issues frustrated me a lot.