Comentario oficial
There is not currently a mechanism for loading 3rd party data. We use the SRTM data both because it is the most universal but it also has good licensing terms that allow derivative products and caching (some private sources don't).
We heavily process the data put it in a format that optimized for mobile use.
We have added and patched data with user supplied data but have limited it to 30 m pixels so far. This is generally done for a one time charge.
We may allow the use of Maps Made Easy created DEMs in the future.