For next years Megabattle I would expect to see the Towering Monstrosity rule played in a way that reflects what we perceive the intent to be. I have a hard time believing people will have a problem with this.
This year no Tyranid Bio Titans actually made the table, so we dodged another question, how to play the Bio Titan's Warp Field.
In the best of all possible worlds, whenever the 40K core rules change, or a new codex comes out for a specific army, GW would review all data sheets and update them to reflect the changes. This is, of course, not the best of all possible worlds. The Towering Monstrosity problem came up due to a change in the definition of 'range'. If as a matter of principle we throw out the old rules and bring in the new, the Towering Monstrosity rule lost all of its teeth. Fortunately, the 45 degree rule has much the same teeth, thus the titans power does not end up increasing or decreasing. A titan is worth pretty much what it was worth before.
With the update of the Tyranid codex, the phrase 'warp field' is reused to mean something entirely different from the old codex. Instead of providing a 6+ invulnerable save to models in a limited area, it provides a 3+ invulnerable save to the single model with the power.
For any critter in the Tyranid codex we should without a doubt use the power definitions used in the new codex. For Apocalypse data sheets, this is not clear. If there is a major definition change or rule change that clearly changes the over all power level of a data sheet, we might consider the original intent, and if necessary run old data sheets under old rules. Otherwise, you end up with data sheets that are priced entirely wrong.
I bring this up in abstract as a point of philosophy, and with a red flag as Cookie is talking about buying a Bio Titan (possibly more than one) and has stated an intent to argue for mixing an old data sheet with a new codex to create a critter very different from the intent of the authors of the data sheet.
One of my old gaming groups used the word 'crock' to describe a rules interpretation that a power gaming rules lawyer likes as it makes his stuff more powerful, but by common sense and intent of the rules is a crock of (expletive deleted). I'd like to encourage Case and Derek to call a crock a crock if necessary.