Helltalons / Hellblades are the Chaos aircraft, they fit perfectly and are what you'd expect an very chaotic and demonic army to use, instead though Chaos Marines have the proper aircraft LaTD get Thunderbolts and Marauders - sorry, what? Why?? This seems madness to me!
If we were dealing with a just turned to chaos army then yes, possibly (though even recently turned Vraksian Renegades have Hellblades/Helltalons), but LaTD are a very chaosy turned army, chock full of demon engines, and demon aircraft fit right in. True LaTD armies can sometimes borrow some imperial kit in their lists, but a lot of the time they don't and it tends to be rather outnumbered by the chaos/demon stuff anyway.
In-case anyone possibly comes back with 'ah but Helltalons and Hellblades are only made on such and such demon world in the Eye or Terror, the other demon engines could be produced locally on the planet' I'd come back with 'really? - you think the cultists can do an A-Team, popping into the a shed for 5 and rolling out with a Lord of Battles?' - look how advanced and demonic a lot of the demon engines are; it's pretty obvious to me they'd actually be produced in The Eye of Terror and shipped / summoned out to the cultists. Or consider the Silver Towers, which come from Prospero itself - if the list has these then Hellblades/Helltalons coming from a particular planet isn't a problem. Anyways; even if you do believe them to be made by cultists on planet, if they can make demonic aircraft like the Doomwings and Firelords then it should definitely be possible for them to make the general chaos aircraft as they look a simpler design.
One other reason is that there is otherwise a lot of cross-over in the models between Chaos Marine and LaTD; defilers and the various demons can be used in each. If someone wants to play chaos, but doesn't collect imperials, he would at present need to shell out for extra aircraft models, rather than being able to use the same for either, which he might prefer to do.
To me having them with Thunderbolts and Marauders is as bonkers and boring as if the main Ork list were only having these as their aircraft 'cos maybe some Death Skullz or Blood Axes nicked imperial planes or some spurious reason. At present I plan to ask my opponents nicely if they mind me using Hellblades/Helltallons, or just not use aircraft if I'm playing Khorne/Nurgle, but this doesn't seen an ideal solution, nor the way the list should be.
I'm setting up this poll to see what people think and in the hope that this might get changed
I'll say why I voted no.
