There has indeed been rumours about DoW being phased out. They where picked up from Alessio himself. The reason is that GW tries to get a better balance in the game and that their ambition is that you should not need more than two books, the rulebook and the armybook, to play the game.
The DoW do mess up balance between armies. Sure, a DoW cannon is not as powerful as Empire cannons, but the armies not given cannon are not meant to have them. They have built in weaknesses, like VC:s and Chaos lack of shooting, that are compensated by them being stronger in other areas like magic and combat, or having other rules. A pair of DoW cannons can throw that balance right out of the window.
Sure, Empire can field 4 cannons and 2 other warmachines, on the expense of flaggelants, greatswords, outriders and pistoliers, but then, if you play Empire today and want to be competitive without fielding the hated Steamtank and Popemobile, you need 2 cannons. Among competitive Empire players, two cannons are a must. They are the only way for an Empire army to reliably be able to handle stuff like Dragons, giants, black coaches and such things.
If you ain´t got a cannon, you might try Mace of Helsturm, but it is far less certain approach. You better have a Steamtank and a popemobile instead. But since many players do not want to field a steamtank or a War altar for fluff reasons (both being hillariously rare, 8-10 steamtanks exists, and only 1 war altar according the the Armybook) people have to put their trust in the great cannon.
The Empire army is made to function around the great cannons and to a lesser extent the other warmachines. The State troop infantry is not the heart of the Empire army, for by themselves they can win battles anymore.
The cannons fullfill the function that VC magic do four you. They are a necessity, a way to give the army character and distinguish it from others. Dwarfs can do without their warmachines (if they put their backs into it) but Empire cannon. Empire is more or less the warmachine army, using combined arms tactics to get the most out of them.
Hence, since GW wants to give each army more specific character, they also try to make that character play for the army. Throwing in something that has been left out to balance the armys strength can potentially break the system and complicates playtesting. Hence, DoW as we know them seems destined to dissappear.
But we can hope that they come back in some other form, as allies maybe, or as an army in their own right only.
