I have a WSP solution which is a subsite with all its content which I want to install on another farm. What are the implications? Is it possible, if so, is it advisable?
If you have wsp file then you can install it to other farm (I am assuming 2nd farm is also on same sharepoint version).
Also make sure you follow the same deployment steps as you did in your 1st farm.
1 thing, I noticed sometime developer use the hard coded URL in the code...so u have to make sure no hard coded URL in ur wsp.
As mentioned here by @Trevor Seward, you'll be able to deploy the WSP in SP2016 as you deploy in SP2013 in most cases.
But please keep in mind the answer given by @Waqas Sarwar MVP.
New and improved features in SharePoint Server 2016 will help you to learn more about SharePoint 2016 features.