Well, when I am going to turtle right now I actually will build up a full RP bar beforehand to lichborne heal so conversion will just be more effective for me personally. I think we can all tell when we are about to get bursted and can build up some RP to pocket for that. Also, unholy PvP already has a sort of rogue mentality to pooling RP as it is so a little adjustment to what you do with your RP to still damage but have a nice RP pool in case you get into trouble will be nice.
5 RP initial, 5 RP per sec for 3% heal (assuming they fix the !conversion macro)... To go from say 30% to 80% behind a pillar would cost you 88 Runic Power and 17 seconds. I think a more reasonable pillar hump is 8 seconds, so you can spend 45 RP for a 24% heal whenever you please. I will take that over a 50% heal every two minutes any day of the week.
Oh, and I honestly have never ran conversion in it's current form but I would assume the only allows base RP regen from skills while active would negate the PvP set bonus.