A bunch of applications should be able to annotate data as read-heavy. Without any change of application code, operating systems can assume that pages mapped read-only should be mapped. This imidietly gives you the majority of executable code and all data files that are mmapped as read only.

I'm not sure how good applications are at properly annotating it, but for most applications assets are also effectively read only.

You don't even need most of the ram usage to be able to take advantage of this. If you can reasonably predict what portion of ram usage will be heuristically read-heavy, then you can allocate your ram budget accordingly, and probably eak out a measurable performance improvement. In a world with Moore's law, this type of heterogeneous architecture has proven to not really be worth it. However that calculus chagnes once we lose the ability to throw more transistors at the problem.