"The problem is not to open the iMac, and yes, I think there are no problems with an SSD instead of the built-in HDD, according to some experience on the web it will take about 10 minutes to open the iMac, take away the HDD, replace it with an SSD, and make it work.
The real ""problem"", is to replace the glue stick to close the iMac properly....
I'm going to buy this iMac, and I'm thinking about the ""adventure"" to replace the HDD with the SSD (like I did on my old Early 07 MBP... (and no, there are no fan spinning crazily or other problem caused by trim or not, and however there's an app called trim enabler...)... But I'm really ""scared"" about this thing of the glue sticks to replace the original glue..."
I put the SSD card into an external case and connected it to the iMac cloned the internal drive to it and started up with the SSD and for ever have used the external as the startup drive the internal drive is on it’s last legs so I don’t even use it.
I know that you can't go from HDD to FusionDrive, because your logic board is not equipped to accept SDD on this model when you buy it with HDD.
Sorry for the incomplete answer.. ;-(
UPDATE
Yes you can....
Kodawarisan had open the new iMac.
there is a slot to insert a strip SSD Apple even on the entry-level model that does not default, it will still find a way to get them or someone so this adapter connector to the SATA classic...
but we don't know if the fan will spin to out of control because of the fact that the sdd won't be from apple. so we might have to cut the fan wire from the sdd
and also the fact that apple does not enable trim for a third party sdd, so if you want the sdd to go to full potential for your new iMac
you have to download a third party software such as TRIM Enabler to activate it.
Yes, it's possible! I just exchanged my HDD for a SSD (240Gb - PNY) and upgraded my imac dec2012 to 16G RAM! Just got very... veryyyy faster than before! First, install mavericks on the drive on a external bay. After that, i'll be set to exchange the devices! I bought a kit from OWC to open and close the imac! Filipe.
