Add a race() function to Tempstream that will take an array of FlatTemplatables and races them - that is, renders them not in order that they appear in the template, but in the order that they are resolved. So

race([
sleep(200).then(()=>"\n200\n"),
sleep(100).then(()=>"\n100\n"),
sleep(300).then(()=>"\n300\n"),
])

Will return a stream that resolves to

100

200

300

This can later be used together with Declarative Shadow DOM for some neat HTML tricks.