I ask you to please connect foot bridges to the road network.
While it might be a long way for OSM Thailand to have usable pedestrian routing there is no point in having it broken in the beginning.
The bridges need to be connected to the road network for routing being able to detect a connection. If you don’t connect it, you’ll explicitly telling that there is no way to get from one way to the other.
3 years ago I went to a meeting at the Portland, Oregon public transit, and they were doing this. Their plan (based on OSM) was to make non-auto transit routable. This includes any foot path.
I would like to point out that cities spend huge amounts of money to private map companies to maintain maps. Portland fired their map company and now use OSM. It seems like Thailand could come to some agreement with OSM to improve the map via shared data and save themselves a lot of money.
Public transport of Munich is already using OSM for pedestrian routing. It is also taking into account obstacles for people with limited mobility (wheelchair, stroller and such).
We just try to make our data best of the world. Applications will certainly come.
We only have to take care to tag things correctly when we add it now. So not only tag something to look like a bridge on the current osm.org rendering, but tag it in a way that the data is correct and usable. So no islands and correct access tagging.