Actually, declarative partial updates (HTML patching) have long been possible in every modern web browser without JS by using my Pure HTML Out-Of-Order Streaming (PHOOOS) technique based on Declarative Shadow DOM. You don't need another syntax with processing instructions. Demo: https://kraksped.pl/phooos/
For GMaps alternative, there are Here WeGo or Bing Maps. For Android, there are Sailfish OS or Ubuntu Touch. For Chrome, there are Brave or Vivaldi (Blink-based). Google is not irreplaceable.