A "Dewar" flask is a well-known gadget (link). An ordinary "Thermos" (brand name) bottle often has a glass Dewar flask inside a metal shell. The flask itself is a double-walled container, with a vacuum between the walls.
Recently I've seen a couple of Ideas here where the authors started by complaining
about how quickly their coffee or tea or sake or other hot drinkable liquid cools. But they have missed the fact that it is not only the wall of the cup/mug through which heat is lost; I'm pretty sure that MOST of the lost heat is a result of evaporation from the top surface of the cup/mug. See the "evaporative cooling" link.
So, I propose that a Dewar-type flask be constructed in the shape of a LIDDED coffee cup/mug. This immediately leads to a mass/stress problem, because the quantity of glass connecting the inner and outer glass shells would be minimal, and could easily break when the inner container is filled with liquid. So there need to be be some small ordinary-insulator (or perhaps better-than-ordinary, such as aerogel) separators, to better distribute the load.
At the top of this cup/mug there needs to be a hole through which liquid can be added/removed. For the first task, we will use a Dewar funnel (double-walled with a vacuum between). The part of the funnel that inserts into our cup/mug is slightly smaller than the hole, so that air can escape as liquid is added.
Since Dewar flasks are usually glass, you should be easily able to tell, even with a permanent built-in lid, when the cup/mug is full. Now you remove the Dewar funnel and insert the Dewar straw, for drinking. This double-walled/evacuated glass straw would have a special "seal" at an appropriate point, so that the hole in the top of the cup/mug's lid is fully plugged, when the inserted end of the straw reaches (or almost reaches) the bottom of the interior of the cup/mug.
The seal is special in that it incorporates a one-way valve, so that air can enter the cup/mug as you suck liquid out through the straw. There could also be a tongue-movable valve at the top of the straw, to prevent the last bit of evaporative cooling. NOW your drink will stay warm for a nice long time!