I think play-off is a good idea. Should be a two-leg fixture though. It avoids a load of dead rubbers late in the season. As for Cobh being hard done by (cue fiddles), well it could be any team. Cobh could be the beneficiaries another season.
As for negating the need for a league - I don't know about that. You still need a league to decide the play-off berths. Its not like Wexford will be getting into a knock-out competition for promotion.:)