Older templates + new features compatibility?

I have been using Squarespace for a long time and went to go make a new site for a client, without realizing how much different 7.1 is to work with, compared to earlier versions.

I noted that you can still use some of the older templates that have the design interface I'm used to/prefer, but my question is, will those be compatible with all of the new everythings that Squarespace is rolling out (e.g., video studio, video courses)?

And if I start down a path with a 7.0 template and find it at some point not supporting the new features, will I be able to switch templates to a 7.1? (BTW I'm disappointed that 7.1 templates are not switchable!)

Thanks!