Things that use HTTP fetch (most of them synchronous at the moment):

client media fetch
^ already replaced with httpfetch_async in httpfetch branch

Serverlist announce
^ already replaced with httpfetch_async in httpfetch branch

engine.download_file(url_target), synchronous
^ replaced with engine.httpfetch(request, callback) API, asynchronous

engine.get_favorites("online")
^ local url = engine.setting_get("serverlist_url") .. "/list"
  engine.httpfetch(url, function(result)
    if engine.setting_getbool("public_serverlist") then
      menu.favorites = engine.parse_json_serverlist(result.data)
    end
  end
^ "local"/"online" argument is removed from engine.get_favorites,
  always reads local one

engine.get_modstore_list
^ instead provide an engine.parse_json_modstore_list(json)

engine.get_modstore_details(modid)
^ instead provide an engine.parse_json_modstore_details(json)