Its actually an open source hardware design built around a Freescale quad core arm CPU. It is definitely designed to be user replaceable; you can print your own boards if you want.
Designing and making boards for this kind of system is very expensive, especially at small scales. The Novena as a whole sold far too little to really spread out the one-time engineering costs and was very expensive as a result. Only 12 of the Heirloom laptops exist and it's unlikely all 12 owners would buy a replacement board; it's just not going to get made unless one of the owners has the skills to do it themselves and is willing to spend far more than the cost of the laptop to do it.
But that Freescale CPU isn't open and cost big $$$ to develop. That's the problem: can't use something like that if heirlooms. Only exception maybe is if whole platform is tied to a virtual ISA. That way, hardware might change but SW & interface is the heirloom. System/38 did this to be ported to successively new hardware and interfaces as AS/400, then iSeries, then IBM i.
I'm surprised it turns out to have an ARM processor - I wouldn't have guessed that it would need active cooling. When you consider that many phones would use this same CPU, in a smaller package with less airflow and smaller heatsinks, it seems even more surprising that a fan is required here.