It was fantastic that ESRI finally opened up the new Map Viewer to be able to add external GeoJSON feeds and have it update in real time. This allows us to link data from other systems without the need for FME or the ArcGIS Data Interoperability extension.
However, it was disappointing to see that any maps with these layers cannot be read by the Field Maps app. Are there plans to introduce this functionality in the near future?
I agree with you that this lack of functionality is important to highlight. I run a live Earthquake Feeds map straight out of USGS's GeoJSON page and it works great, but my team is asking for an actual App for all our users, and I was sad to have to tell them that we have to stick to using just the WebApp link URL.