Multi Replications Plan on 2 servers
Let me give you a very broad piece of advise: I think you are trying optimisation in the wrong way. You are doing "We have spare memory, let's use it for something else" (which is otherwise very lucky and many people will envy you) instead of "let's identify our bottleneck and fix that with our resources".

I am not telling you that your idea is wrong, but in general, scaling out with slaves does not provide a better latency (and in many other cases, clustering it reduces it), but a better throughput (which if you were under high load, can sometimes mean better latency). I do not know if that is a problem that must be solved in your case. While having multiple mysql servers in the same machine is common, for example, in the hosting industry, they do not do it for performance, but for a cost-saving reason (consolidation). Also have into account that you may be more than doubling your maintenance/administration costs.

My real advice would be to identify your bottleneck: latency, throughput on where? Memory? Disk? Network? And try to use the extra resources in the best way- Are temporary tables being created? Can we use ramdisk for that? Are many queries too slow even if they are executed on memory? Can we setup a on-memory key-value cache system (memcache, by the way, integrated on MySQL 5.6-InnoDB) for caching results of frequent queries? Your write throughput is maximised? Maybe you need sharding. Your read throughput is maximised while your write throughput, network and disk bandwidth is low? Maybe your idea is ok. But you need metrics in order to support such an important architecture decision.