Does that mean that scripts (tags, extensions, etc) are all loaded in paralell? (So that the limit of 6 calls in http, will be changed in http 2)
Or does this just load the container tag as a single file, so there won't be a change in timings?
How resources such as tags are delivered to the page will depend on the configuration options in your TiQ setup. For example, you can choose to bundle tags with the utag.js library or have them delivered stand alone. With regard to extensions, they are either included within utag.js or scoped to a specific tag (thus bundled within the tag code).
So the answer to your question is, it depends on your configuration. If you don't bundle tags and then utag.js loads, then loads 40 other individual resources (such as tag templates) than those will all load in parallel.