I believe were not all on the same page of what rank1 Frostbolt meant. To me it was the combination of a quick slow and it being spammable. Hence Early Frost isn't exactly the replacement for it.
But I've mainly used rank1 Frostbolt in TBC, I havn't used it as much in WoTLK because of the large amounts of haste.Hence it would be nice to have a rank1 Frostbolt, but I wouldn't mind to see how pvp will go without it. I do believe that increasing the range of Curtain of Frost will help a lot to replace rank1 Frostbolt on catching the flag carrier / fleeing player.
You're right, we're on different pages if you're thinking of rank 1 simply as a faster snare. Frost pvp in wotlk has never lacked enough mobility or tools such that rank 1 was all that important to save time on a snare, especially in the confined space of the arena. Rank 1 was mostly useful for quickly covering a target with both the slow and winter's chill prior to a polymorph, so that the first dispel had a much smaller chance of removing your CC, especially if the only enemy dispel was a warlock. Since winter's chill is gone it won't work the same even with early frost.