The news was revealed by Microsoft's Windows Insider head Gabriel Aul on his Twitter account:
Good news for Lumia Icon owners: Icon will be supported for Windows 10 Mobile Preview builds from the Dev Branch in the near future. Yay!— Gabriel Aul (@GabeAul) May 5, 2016
The Lumia Icon is virtually identical to the Lumia 930 which does support the Windows 10 Mobile update. We recently decided to try to update the Icon to Windows 10 Mobile, via the Windows Insider app from the Store on the Release Preview channel. We found that it did indeed work.