To see why a core would be useless, we must ask the question "For what reasons do cores exist at all?"
The answer is as follows:a core is the entry point to control of the ship, is the thing to take out to kill the ship, defines docking positioning, and identifies the ship in the universe.
A control chair utterly eliminates reason number one.
Yes, mostly because controlling a ship from what is apparently a computer core that doesn't even have a monitor makes no sense.
Reason number two becomes silly (if we're not shooting at the pilot controlling the ship, why does hitting this one block kill the ship? Does it have no backup systems at all?).
Backup systems would actually be a decent idea, but I guess it kills the ship because it's the only computer core. However, shooting a computer core shouldn't blow up a ship, merely disable it and make it salvageable; you should have to hit a ship with tons of explosives to make it just go boom (Or the ship should have to have an explosive reactor for a power system)
Reason number three is something that is absolutely a bad reason for cores to exist, as it severely limits docking for ships that aren't built from the start around having the core at the center.
That's due to terrible docking mechanics. If ships docked via clamps (or, in the case of turrets, hinges) we wouldn't even be thinking about this.
Finally, reason number four is just a quirk of the game (Space Engineers does just fine and dandy without any equivalent of a ship core, you can even just split a ship in half and the two halves become separate ships.).
I dislike this as well.
Cores just don't really bring much to the game, and a control chair raises the issue of cores by taking over the piloting ability that is the only real necessity of cores. We could just have cores be changed to be two blocks tall and show a player if one's inside, and have a chair shape. The only differences then with the suggestion would be due to the whole player dying with the core thing (maybe a good reason for seperation, but I do feel it's rather silly, plus you can just exit the core before it gets damaged if badly losing) and the docking effects (a secondary concern that's moot if chairs get placed near the center or you have a bunch of docking enhancers and room anyways).
I dislike chair cores because that means that you can't have your chair (command access point) and core (Ship build starting point, center of rotation, and main vulnerability) in two different places. If I want to build, say, the USS Enterprise, and put the core in the center of the warp core, but the chair at the top of the saucer in the bridge, I should be able to do that. In addition, even if I get out of the core before my shields go down completely, all (or at least many) of the shots will be headed towards the core, so if I'm stuck near the core when the AMC bullets break through the hull, I'm very likely to get hit, compared to if I'm in the front or on the top of the ship, which I could orient so that it isn't between the enemy ship and the core. Also, it's kind of hard to have escape pods if you need them to be in the one area where they'll probably get obliterated. :\
I suspect we'll be stuck with the magically-inside-blocks thing for years to come and won't even get something as simple as chair cores.
That would suck terribly.