If the 20 team proposal means that teams can be promoted and relegated from the top division without fear of a total implosion, then this should be good for the stability of the game. Of course, this would mean fairer distribution of money across the two divisions, a point the top teams might not like.
The second tier would certainly become more marketable and could generate a TV deal in its own right.
I fear for what may happen to the rest of us. Six teams in the present Championship would be cut adrift plus the 10 sides in League One. A 16 team league would probably be too big whilst an eight team league would be too small, or it'd mean 'splitting' halfway through the season which is a pain in the backside.
If we do get promoted this season, the challenge of making the top six in the Championship at the first attempt would be very demanding indeed.