- There are two types of pieces: stones and ghosts. Each player uses stones and ghosts of their own color.
- A group is a maximal set of orthogonally contiguous pieces of the same color and type.
- A liberty of a group is a point orthogonally adjacent to it, provided that said point is either empty or occupied by a like-colored piece of a type different from the group. For example, a white ghost is a liberty of any orthogonally adjacent group of white stones, and a white stone is a liberty of any orthogonally adjacent group of white ghosts.
- On their turn, a player must perform exactly one of the following actions:
- Pass.
- Place a ghost of their color on an empty point.
- Place a stone of their color on an empty point or on a point occupied by a ghost of any color. In the latter case, said ghost is then removed from the board.
- Area scoring is used. On-board ghosts are added to the scores of their owners.
- For the purposes of ko and superko rules, two positions are considered identical if both have pieces of the same colors on the same intersections, even if piece types don't match.
I think ghost placement will only be desirable on seki intersections. Other than that, games played under these rules should look much like normal games.
Note that, without seki, fractional komi isn't needed, as there will be no ties.
Example
Whoever moves first here can capture the enemy stones. If Black moves first, they can capture by placing a ghost at either b or c and, on their next turn, a stone at a or d, respectively. If White moves first, they can capture by placing a ghost at either b or c and, on their next turn, a stone at c or b, respectively.
before they can play atari at a, and by that time they are in atari themselves.
with a ghost placement at a, which puts only White in atari. If White answers 
with a ghost placement at a instead, Black simply gets