you can replace the iMX6, as I did a couple of years ago (and not had any issues, except the ‘initial startup’ issue I mention) in the post about this here
the quad imx6 is slightly less powerful (1gz vs 1.2ghz) but had a bit more ram.
however, you miss out on the other benefits of the organelle-m.
- speaker, mic
- battery power
- trs midi
- newer version of linux
organelle-1 uses pretty old version of arch linux, which is less compatible with other hardware, and more difficult to add software to … I did start a project to upgrade the linux, see here but never had time to finish it off - perhaps one day 
but for sure, if you have an organelle-1 its a good upgrade - and will become more attractive to end-users if patches start making use of multi-core/more memory.
(as I mentioned in my above thread, up till now, mainly Ive been using the quad for development purposes, as I wanted to create patches compatible with ‘factory’ organelles)