Too bad ? An example demo by gpx file is available and the method is simple to implement.
But, given that no one implements it, it's not useful.
You aren't making sense.
No one was saying it couldn't be done.
The OP was asking about being able to use a Garmin device.
Going on about stuff that can't be done on a Garmin is useless to the OP.
It seems that one thing (Locus Maps) supports what you are talking about.
So, complaining that Garmin is not "participating" makes no sense because no one (other than Locus Maps) is participate either.
I use Locus Maps by-the-way. The developer puts lots of effort into adding features to it.
You are imagining all the "pitting against each other" stuff. No one is doing that.