So, this is something we're NOT seriously considering yet, but I'd love to hear feedback as always, as it popped into my head.
What if, instead of banning or allowing lords of war through the creation of an exhaustive and potentially difficult-to-maintain or confusing-for-players list, we instead took a page from the Narrative in 2014 and tweaked certain D results and (optionally) stomps?
These would be two separate questions:
1) Adding a rule that simply prevents weapons with a hellstorm template or blast larger than 5" from reducing a cover or invulnerable save to worse than 5+
2) Adding a rule that allows models affected by a "6" on the Stomp Table to make an invulnerable save if they have one, at no better than 5+
I don't know that #2 is really necessary ... though Stomp certainly has its opponents (especially the large blast stomps of the Tranny C'Tan). The tweak to the Hellstorm Template and D-track of the C'Tan would still make him fairly preeminent at dissolving magic-powered deathstars, but might substantially reduce his ability to willy nilly remove entire squads of regular joes and other things.
Food for thought.
This is in contrast to a ban-list of certain Lords of War and/or Lords of War weaponry, should they be permitted in the Open.
Keep in mind these things are still being discussed and finalized, and you should offer your input freely, but without fretting that you need to bombastically prevent (or force) adoption of a rule that is not a rule yet (or really more than a pondering).
Edit - note, this would not be crafted, if ever done, in a fashion that would allow people to combo shrouding and/or stealth on top of the reduced save to kick it back up.