Decidability of the language of all deterministic LBA where all states are reachable
After days of constantly refreshing this page in hope for an answer today I woke up and my very first thought might be it.

If all states are reachable and it is deterministic this means there has to be a set of inputs where every state  will once be reached.

semi-decidable Algorithm:

Validate if DLBA-Encoding and reject if not;     # returns 'no' on bogus
k = 0;
Repeat until every state has been at least once been reached {
   For every possible input w for the DLBA of the length of k {
      Simulate DLBA with w for g(M,k) steps while keeping record of the reached states;
   }
   k++;
}
return 'yes'


It will accept if all states are reachable

It will reject if not a valid DLBA-Encoding

It will run forever if valid DLBA but not all states are reachable

I figured out, that DLBAs can have states where there are a series of transitions leading from the starting state to those but they still can never be reached.
So just looking at transistions isn't enough