Cloud Computing

Cloud computing is an internet-based computing that provides shared computer processing resources and data to computers and other devices on demand. It is a model for enabling ubiquitous, on-demand access to a shared pool of configurable computing resources (e.g., computer networks, servers, storage, applications and services), which can be rapidly provisioned and released with minimal management effort. It is in demand, if you are planning to take IT infrastructure management as a career.

You can be a cloud analyst, cloud architect, mobile application developer, cyber forensic analyst, etc.

Both of the subjects are not a specialisation at BCA level.BCA is a graduation and it cannot have such a micro level specialisation as they are subsets of a bigger part of computing.
Few institutes like CSSRL may give you an additional certification from UK and a BCA degree from IGNOU.
Successful completion of the IGCS program entitles a candidate to receive an International Diploma in IT security accredited with IADL (UK) and Bachelor's degree in Computer Application from Indira Gandhi National University (IGNOU), Delhi.

Yes, it's a good course to pursue after class 12th.

In my opinion, Internet Of Things (IOT) is going to be the future. Actually above mentioned subjects are all related to IOT. You need to learn these technologies to get into IOT. You can also look for courses on these topics in Coursera.

Cloud computing and cyber security is more demanding stream but it's tough to make career directly in cyber security cell. Could computing and big data analysis is recommended according to me. MCA is also good in IT field as it has so many job opportunities.