What high-level problem are you trying to solve?
When starting a Geotrace or Geoshape the enumerator is faced with a map screen which looks very similar to the geopoint screen (with map or placement-map.). There are no instructions on screen and it is slightly counter-intuitive to tap a marker icon to start the process of recording a line or shape (and that this is just to choose which recording option to use). Sometimes even for old lags, it is not immediately obvious which process is required, especially on a form that collected multiple geometry types… If you had enumerators that were running on auto-pilot for example 
I know we’ve discussed easing the process of recording the vertices and that might take some time to implement changes in terms of form design, my idea here is (I hope) more simple to help enumerators get going…
Any ideas on how ODK could help you solve it?
Suggestion 1: add text at the top of the screen (similar to that available for placement-map option for geopoints). For example
“Tap the Add Marker Button to start recording your line [shape]”
Suggestion 2: Change the ‘Add Marker Button’ icon to a line or shape icon depending on the question type.
Suggestion 3: Suggestion 1 + Suggestion 2 - and change the text accordingly to match the icon to tap 
Hopefully these don’t require any major changes to code or XLSForm spec…
Side note - the Docs currently use an old style of map interface where the buttons are in different places / order. Maybe not a high priority, but it would be good to update them too.