I've just checked in the last pieces of the migration to a new data-structure for vectors, called "basic-vectors". The most important new feature is that the vector's length is now a fixnum, so that vectors are now restricted to most-positive-fixnum (#x1fffffff) rather than the old limit of #xffff.
One practical consequence of this, is that the example GC implementation in los0-gc.lisp is now capable of supporting new-spaces up to size 2 GB. However, I believe the practically useful range is going to be below a few tens of MB. I've set the default size to 2 MB.
There have also been numerous bug-fixes. A new los0.img is being uploaded to the clnet web-site.