AP + HP is fine, then you have flat magic pen = good for assassins/burst mages against squishies. But then there is also a %hp dot that gets stronger if the target is CCd = good for control mages against tanks.
You could make one build out of 
+
+ 
(7-10% move speed, 15 or 20 magic pen, AP and HP) for burst champs.
And one out of 
/ 
+ 
+ (Liandrys passive, 10% cdr to apply it more often, AP and HP) for control/poke/dot mages vs tanks.
I'm not saying the idea itself is bad... but..
how bout we fix the trash AP items BEFORE we mess with the few left that still actually work
AP itemization in general has a ton of items that could easily be split into several. Liandry's is one of them, and on top of that I think Haunting Guise really needs at least one more upgrade, as currently it railroads players into building just one single item. AP assassins and fighters need to start having their own itemization, distinct from mage items, and I think Liandry's could be a good start to work towards updating magic pen and AP + health combinations.
"Please remove one of the few DoT niche items to satisfy burst mages."
all benefit from it, then come standard DPS mages and niche cases like: 
hell even AP 
can use it (but riot killed him anyway).
Magic pen isn't only for burst. Singed really benefits from Magic pen.
Also why should an artilery mage item get HP?
Liandry's does not need to be removed, Haunting guise just needs a non-dps/DoT item to build into. This can then have flat AP and higher Mpen.
Can we please not start throwing CDR on every "control mage item"? Otherwise it's going to end up like enchanter support itemization.
I wish that AP assassins had their own itemization that isnt the same as AP mages. Im thinking of the fact that we have lethality for AD assassins, Crit for ADCs (and yasuo), and things like Cleaver, Gage, Hydra, or Triforce for bruisers. Having items that are good for actual mages and different ones for ap divers and assassins seems like a pretty good idea.
Only main problem I see is that if an item is better for the opposite ap class than what it is meant for, things could get unbalanced quickly (like lethality being built on basically every ad champ for a while). If they could make this happen, it would be really cool and I would probably have a lot more fun with AP champs. As long as they dont fuck it up (which this is riot, so they probably would), this would be a great addition to league.
Ok say riot splits Liandries into two items, then what happens to champions like 
and 
who build the item as part of their core? They have burst damage and consistent damage, you can't just split items without thinking about how it affects the game as a whole, Riot understood this firsthand when they removed Brutalizer and made it into 
and 
How about no?
I think it's fine as is. Liandry's is kinda meant as an off-tank AP item (most damage champs would prefer raw AP over the burn, with the singular exception of Brand). The issue right now is that Liandry's is one of the only items that offers both AP and flat pen (perhaps the only? I don't really remember...). Riot needs to expand AP itemization BADLY too keep up with how many options AD scaling champs have.
No CDR please. Why add CDR when the games saturated with the stuff?
But why split it though? You never say why
the reason liandrys came to existence with those absurd stats was because there was once upon a time when tanks stacked HP and no resistance. If liandry gets changed according to your suggestion, it might be possible that we start seeing HP stacking, 0 resistance 
tank assassins due to their dmg scaling with HP depending on how the rest of the AP damage gets changed on season 8.
that will a huge nerf to teemo though. LOL, fuck it screw the lil' bastard.
no liandries buffs pls
The only fear is that mages would build both and do true damage like crazy. To combat that I think making it so there magic pen does not stack would be a good addition.
