Both XFES 2.0 and 1.1.7 will support Elasticsearch 6. It's possible XFES 1.1.7 will support Elasticsearch 7 because of these changes, but it's unlikely that we will officially support that version, though we can only guess based on their published deprecation approach. We would certainly intend XFES 2.x to support Elasticsearch 7 (and 8) when those versions exist.
In terms of the changes we made, where necessary, we will still be using one index so the behavior is basically unchanged from previous Elasticsearch versions. We will now track the type within a field in the index for relevant versions (for anyone running ES6 with the new requirements, which doesn't include indexes created in ES5). This will be invisibly handled in most index-related operations so existing indexation code should continue to work in many cases. Searching and limiting to a specific type requires a different set of filters, but if you use the core XFES code to do this, it will handled for you.