So is it accurate to assume that there is no way to complete the achievement for Uber Doom Skulls for at least the next 10 weeks, maybe longer? This surely can’t be the case. Why have an achievement you can’t actually complete?
Or am I missing a way to generate these skulls somehow?
You can complete it, but you have to wait for the campaign to be over. I have no idea what achievements there are, but it would be similar to an achievement for participating in a Tower of Doom event, a Raid event, or an Invasion event. In all such cases you just need to hang out until the game gives you the opportunity again.
Unlike with the new faction rotation, at least we have a decent idea about when Uber Doomskulls will return to the game.
One of the random storms creates uberdoomskulls, see [REPORTED] New Storm Needs Appropriate Label.
However, I don’t know whether that storm is turned off when uberdoomskulls are turned off. I just played a few matches with the Chaos Storm talent, but didn’t see an uberdoomstorm (had 3 bonestorms and 2 doomstorms). Even if you can get the storm, you’ll see it so infrequently grinding the achievement will be a real chore.
To get a random storm, either use the Stormsinger troop or the Chaos Storm talent in Archmagus, Barbarian, Deathknight, Dervish, Frostmage, Stormcaller or Titan.
Seems like a really weird choice to turn them off at all 
Are we to understand there can only be one kind of Heroic Gem at a time?
I think this is the idea. Which I’m not opposed to as if you have multiple HG on the board at a time it could really make the game a mess
I tried to create an Uber skull storm using the chaos storm talent to no avail. I guess they are turned off and will not appear.
Waiting 10 weeks to finish this achievement is one thing, but it is not certain that they will reappear then…there are supposed to be more of these type of gems coming, and the new campaign will probably have a new one. I just wish I knew this was going to happen before they took them away.
Note: This means you have 9 weeks left to complete Lycan Subscribe achievement…
You can grind the lycanthropy one out in a few minutes with thrall + 3 copies of this week’s troop that passively generates the gems. Destroying the entire board counts as matching the gems, so just keep casting thrall and start a new battle if everything dies.
I would assume uberdooms are going to be the gem for the week in between campaigns for tower of doom