I'll always vote for a reduction in the "switch mark" cost.
Reasons being;
1} It needlessly limits gameplay.
2} It introduces a penalty on deck experimentation.
3} Charging electrum to switch your mark offers no added story to the game, and imo, detracts from it.
4} Friendly PvP is that much more difficult to enjoy when you must pay out electrum to change deck with no gain back.
5} Slows the rate of change of variety of the game; if I'm bored of Farming I'll switch to PvP. This often happens right after I buy an upgrade or if I've just lost a string of games, meaning I'll be low on cash. If the amount is below what it costs to switch marks then I'll probably log off for the day and wait for the oracle as opposed to playing the game.
Aside from that PvP enhancements are always great - recent ones were fantastic