I actually googled this and I have found nothing; blame google if you want.
to be more clear: this is NOT a suggestion topic. here we discuss, with what the game gives us, of the plan that the devs have. if they have still one. because, I think shadow liars are the prelude to the core. or, well, the unknown passage. I'll explain later in the topic.

what do we have? the 30 in the gate map, the lobby, the fact that they didn't edited the core level name.
about the name. "the path is sealed" to me seems very similar to "the path is open", which will be after (or better, if and when) the core is opened. same for the 30 in the map. only confirmations on the opening of the core.
now, about the lobby. two useless elevator platforms (you know what I mean?)? that reminds me of emberlight and the manor. and all those screens remind me of emberlight, where some of the gremlins are watching screens. also, the screens on the active elevators. so, what is it? well, there are many. someone counted them? how about a comparison with the number of the existing levels? you get it? no? I'm not sure on this, so let's go on.
so, if all those screens are the actual levels, there may be all of them in the core. which means, in the core there is everything. if we get inside, there might be levels with all monsters inside. ever-cycling clockworks to the max. surprising? not so much. thinking for a while makes you realize that, even without the core. in fact, where are all those levels coming from? entire planets swallowed by the clockworks? where is the magma? nah, whatever has built the clockworks has made all types of terrain and eviroment for... mmm. this controversal, I'll keep it away.
now, what if those things are something else. what could they be? what fits in the screens? knights faces? what use? idk. pure white as the pure black of the swarm? that might be. what would that mean? just a gigant energy source? why putting it into a gigant lockbox, close it and throw the key in another dimension? a force that destroys the swarm? gigant lockbox question again.

ok, this ends the part with no spoilers. if you are cannot enter the 5* hall of heroes, I suggest stopping now.

2 things make me think: when you defeat the rj (or the rt, I don't remember) your fella that talks slowly (can't remember the name) tells you of the feeling that the knight actually could belong to cradle and that they should not go away. this is the feeling of many knights. stated as absurd, but still, it's something.
also, said by Lieutenant Feron: the structure of the clockworks seems more to be keeping something in than keeping something out.
so, it's something that attracts you and that must be kept in a gigant lockbox. a sentient, possibly evil being? "but, the light..." yeah, the light at the end of the tunnel is death, my dear. fishes in the depths use light to decieve their pray before swallowing it.
Edit1: from the echo stones: maybe not so evil. but I would like to see myself.

I don't think that the sanctuary is in the core; I think it is just a piece of what it is in, sent by the core.
about the alpha team: the swarm was there to reach the core or was it just chance? the core: was it chance or something else?

the echo stone is (imo) a message from the core. which means that it must have some protection or its energy would be absorbed. the unkown passage it's the swarm that attacks this protection.
also, the SLs are the only levels that don't cycle (well, missions too, but whatever). they are always there, no matter what gate you are. so, the swarm uses them as base to get to the echo stone. and for "uses" I mean "makes them remain still".
the gremlins made the clockworks? I stack on what feron said: no matter how industrious they can be, they can't build a whole planet. someone/ something else must have done that.
the core was open when the alpha went in, and there is a recon module, so they can't be died just by watching the light.
the skylark wasn't attacked. it was (from the recon module) "pulled on cradle".