Recent updates to the game have indicated that work is ongoing for Warcraft Rumble PC support!
The latest client build has some files that indicate work is being done for desktop input to the game. A recent update to the Battle.net App Catalog also added a developer-only product for a Desktop version of Warcraft Rumble.
Both of these things together indicate that work for PC support may be ongoing. This doesn't mean it will ever release to players, so please keep that in mind.