I have been thinking about doing those things.
Adding an option to manually enter latitude and longitude for a map image point should not be very difficult to do. I just have not got around to adding it. But I'm sure I will eventually get around to it.
The option of using the current GPS location for a map image point coordinates is a bit more tricky to implement. It requires storing the incomplete map after the first point is selected until the user applies a second point. During the time between first and second point it probably would be good to be able to display the map, but the user might also want to put the phone away. And if the user switches to using other apps before adding the next point, there probably should be a way for the user to select the incomplete map which is not very useful for navigation before the second point is added. Right now that app only deals with completed maps that have at least two points selected to provide location, orientation, and scale of the map image. So that request is a usability challenge. I have some thoughts about it, and I think this would potentially be a very useful feature when a network connection is not available. But at the same time it will be difficult for the user to know how accurately drawn and scaled the map image is, since they cannot preview such a map over a Google Maps view.
Finally, I will most likely not release a new version of Custom Maps before the April/May time frame to allow all current users to upgrade their apps, and use them at least once to get their existing maps transferred into the new storage area. As far as I understand the new Google Play Store rules regarding storage access, no future version of Custom Maps will be able to read the /CustomMaps directory in the public internal storage. So I will probably concentrate on improving map management features: importing and exporting maps.