Now I'm working on a new Drupal 8 module "LandingPage Framework". By the fact it's a package of several modules and themes.
Project page: https://www.drupal.org/project/landingpage
I still don't have a stable release but there is a version that you can start to play with and let me know if it worth to continue the development. The module use the power and the magic of Drupal Paragraphs. Paragraphs approach provides beautiful flexibility in content management because you can get any Drupal functionality in paragraph entity and you can set paragraphs on each page in individual order.
The main goal of that package is simplification of Drupal based LandingPage development. I want to provide several out of box solutions that can cover the main cases of LandingPages such as Event page, Product page, Promotional page, CV/Portfolio page etc. But I want to provide extremely unlimited options to customize the page.
Please visit this page to take a look on very simple example of Landing page build with that module:
Also you can get more specific technical information in README.txt
I'm not going to write a long post, because one image better than 1000 words.
Please see a quick screencast in that post, it's only an introduction that allow you to catch an idea. I hope I'll do the serious of screencasts to explain how you can use LandingPage Framework, how you can customize LandingPages and how you can do your best in Responsive Design.