If so, this is a pretty drastic design flaw in my opinion. I am the GIS Admin at my org and I have migrated to Pro. I have ten other GIS users that have yet to make that transition to ArcGIS Pro, however. I am attempting to recreate my old attribute assistant workflows from ArcMap in Pro. I was able to do so but immediately noticed that when I opened an old map from ArcMap, that the data source was broken. When I attempted to point it to the feature class, nothing happened. The little red exclamation point remained. Is this intentional or am I seriously being forced to use ArcMap until I can convince 10 people who have been using ArcMap for 10+ years to upgrade? They are extremely unlikely to upgrade, so it seems like my hands are tied unless I just force them to make the upgrade. I would prefer not to force anyone to do anything. I've been making the case for users to switch and believe they will do so when they see fit. Not to mention transitioning and training 10 new users of ArcGIS Pro would be a pretty substantial time sink for me.
This backward compatibility has been an Idea on GeoNet for years. This definitely makes the upgrade from ArcMap to Pro much more difficult.
Hopefully you can create a feature service from the upgraded data and have your ArcMap users utilize the feature service until they have been upgraded to Pro..
You wouldn't happen to have a link to that thread, do you? I'd like to follow it. I looked before I posted this topic but couldn't find it. Parcel maintenance is literally the only workflow I have not moved to pro. I would really like to do so, but I am not willing to switch to the parcel fabric yet for a number of reasons. It's a shame that something as silly as this will force us to continue using ArcMap.
Here's a poll that gets into this topic:
An older thread as well: