What are the job prospects for people interested pursuing an MS in computer architecture? Is it mainly research or is there scope elsewhere?

As far as I know, there is no MS offered specifically for Computer Architecture. You will need to do an MS in EE/ECE/CS with a specialization in Computer Architecture. It is definitely recommended to do the introductory and advanced courses in Computer Architecture even if you are leaning towards a Systems related specialization. This is because you still need to have a good handle of how the underlying platform or HW works and system software closely interacts with the underlying platform. Most of the jobs post an MS are in chip verification/validation/design roles in the front end. There are a handful of jobs in Functional/Performance simulation, Performance Analysis or Power Modeling, but these are hard to get into directly after just an MS. Phd graduates or MS graduates with prior relevant work experience are generally preferred to these roles. Potential companies that you can get into are AMD, Intel, ARM, Qualcomm, Marvell, Oracle, IBM, Cisco, Mediatek, Nvidia, Apple, Google or really any company that has semiconductor IP and needs to do architectural spec, RTL design and verification. Although there are several RTL related roles, pure architecture roles in the industry is something of a niche area...