You are saying that the Jabberslythe is a game winning monster, I have taken it in all of my beastmen armies so far and honestly... its not as effective as you think it is. It can't stand on it's own two feet in a fight because it has no armour or saves of any kind, it does more damage when it looses wounds than when it attacks because of its poor WS and it has too play a very stealthy game of hiding behind the terrain to avoid any cannons/bolt throwers/warmachines which can rip it appart.
It's only redeeming feature is the aura of madness which honestly hasn't done alot for me, I've killed a lone mage with it by scaring him, but a turn later I dropped right in the heart of an empire army (with the empire general on the other side of the board chasing down Gors), affecting 5 units and nothing happened to a single man. The Jabberslythe is too inconsistant to be a game winner, but it can be a line breaker. If you want a game winner, look too the hydra to blame, leave little old jabber out of this...
As for an apocalypse game in warhammer, I would be looking forward too this, because I have played a game of 40k apoc, I know it can be alot of fun and a great way to waste an afternoon with friends. Dont believe me, we spent most of that day laughing at the ork player who thought he could deploy his army in 3 minutes... then left half of his army in another room until someone told him it was there.
But I think GW already tried a half baked release in WD, something about "Time of Legends"? I can't remember the name but I do remember the phrase, "...as many cannons as you want..." being used somewhere in the article.
On the subject of armies vs groups of monsters, I am on the side of the armies because I love lord of the rings and the uruk hai especially. But I think that using an apocalypse game in warhammer would allow your army to have both massive amounts of rank and file and groups of monsters, making for an interesting game.
If your opponents are just playing monsterhammer, find new opponents who share your love of rank and file.
If you yourself are playing monsterhammer, grow a pair and drop the monsters. If you truely want too show GW that you want rid of monsterhammer then don't play monsterhammer. Force yourself to take rank and file and to hell with the consequences! So you loose a game... who cares? If you don't want to play monsterhammer, don't play monsterhammer.
Seige rules are in the general's compendium as well as naval and the old rules for running a campaign. It is one of my favourite books in the history of GW because it brings more of the hobby in too the game. e.g.
"Want to get your goblins drunk on fungus wine? Sure, make up your own unit that dispences drinks before the game and gives you D6 fanatics in every unit as well as having MR (1) to give it a purpose in battle! Since there is no model, why not convert one?"