I would also be interested in this.
Even if it's just a little heart with the last heart rate reading the watch takes. When you tap it, it could open an app and immediately start another heart rate reading.
I love the heart rate monitoring of the watch, it's the main reason I got the watch. Unfortunately opening the glances is sooo slow for me no matter how few glances I have set up on my watch.
I really wish a developer could develop an app/complication like this. Just an app that looks like the standard heart rate monitoring and still writes to the health app.
It's crazy a lot of people complain about apps opening slowly on the watch, but I have a bigger problem with glances lagging badly.