I\'ve partially discussed this solution in my thread here: http://star-made.org/content/simple-solution-hull-mechanics
But to spare you the wall of text, it detracts from customization and is actually kind of goofy.
In my thread it was slightly different, mass-based hull-strength, though the result of your solution and that one is pretty much the same. The problem is that I could essentially have a 100x100x100 block of filled in hull anywhere on my ship, but then if I surround my core with only 1m thick hull, or no hull at all and leave it completely exposed, you\'re either spending a long time sniping the core or just chipping away at hull.
Essentially what it comes down to is, if I make a big ship or whatever, it\'s not as beneficial for me to thicken the existing plating, than it is to just build big blocks of hull on various other places on my ship to boost the HP of my ship core. It\'s less emphasis on protecting your ship by design, and more on protecting your ship-core with hull spam.
I think that you should protect certain parts of your ship by designing your hull around it, and thickening the hull in places that you prefer to be more armored. This type of depth allows for design flaws and \"Weak Spots\" based on someone\'s design. In your proposal this isn\'t the case.
Now Ixalite said missiles would have more value in your proposal, and I agree but only to a small extent. The heat seekers and BB missiles are only marginally increased in value. Since you can essentially have your ship-core exposed and just tank the damage as long as you have bricks of hull somewhere else, the design of ships will become more about protecting big bricks of hull rather than protecting the ship-core. And since lockon missiles only aim for the core, d1000\'s are potentially the only missiles that increase in value here, and since ships move, it\'s going to be pretty damn challenging to hit what you want to hit with a d1000.
However, I would agree that \"Core Drilling\" as a tactic also detracts from the depth of combat a lot. That being said however, there are a few other viable solutions to making core-drilling a less punishing and less viable tactic.
For instance, having the radar signature on your ship be the center of dimensions, rather than the ship core.
I also have a thread with a proposal for ship cores here: http://star-made.org/content/overhaul-ship-core
And there is yet another idea about having the ship core overheat after a ship loses a percentage of its integrity(Total blocks).
All three of those ideas for the ship core have their flaws(Personally I think the radar signature solution is probably the best one), but those solutions don\'t necessarily introduce cheesy ways of building your ship. And they all add some depth to combat in one way or another.
Just to re-iterate, I agree with your intent to make core drilling a less viable tactic, I just think that there are less negatively impactful solutions out there that accomplish that goal a bit better.
That\'s my constructive feedback!