PVP can never realistically work in D3 as it did in D1 (zomg golem fights were so great, and ear farming ofc). D1 had entirely balanced skills, in that all classes drew from exactly the same skill pool, but could use books to improve each spells power. D3 is very different to this, there is no current ability to further improve a preferred skill, which in turn leads players to seek out only those builds which are deemed the most powerful (zuni + jeram, or jade + quetza WD, mara 6 DH, or any crusader build focused on a flail leg effect). The root cause of imbalance is NOT legendary effects (this will change with legendary gems, which are all severely overpowered, to the extent that 1 leg gem > the rest of your items combined - I'm looking at you smite gem/conduit gem).
In order for PVP to become a realistic possibility, numerous drastic changes are required, they are explained below.
Class balancing: A WDs relative power must be comparable to a monk's relative power, and the same must be true also for the crusader, wizard, demon hunter and barbarian. There would be no reason to fight a WD using a monk at this point in time due to severe differences in power.
Element balancing: Each element within a given class's repertoire of skills must be aligned with a particular play-style, allowing comparable synergy, and enabling build and play-style diversity. Basically, 1 element may serve as a support role, one as a tank role, one as pure dps, etc. These builds would all need to have comparable power (this would promote group pvp). An additional suggestion could be to rework +% ele dmg, as this stat heavily restricts all classes and builds (essentially forces all skill runes to be of the same type unless they are pure utility skills), this stat would work fine if skill rune elements were aligned to begin with.
PVP damage balancing: A shield bar could be added (is used in many pvp focused games), this shield is only used within pvp combat, and once depleted, pvp attacks would reduce a player's hp. This would help to draw out battles, so that you are not simply 1-shotted. PVP should be more drawn out, allowing for a short burst DPS build to be played off against a high armor sustain build, a DoT build, or builds which require multiple summons/recast on semi-lengthy cooldowns (mara 6 for all sentries up). This would ideally allow enough time for any given class and build to prepare its best case scenario (unleashing 1 builds full potential against another class, which is doing the same). It is quite likely that dmg mitigation would also need to be factored into PVP balancing as buffing player HP substantially to compensate would ruin PVE.
Additional suggestions: PVP sets which provide PVP focused stats and effects, attainable through PVP combat (win = x tokens, loss = y tokens, item roll costs z tokens - similar to kad gamble). I would also second a mixed pvp/pve scenario, as suggested by kempfer91, this may appeal to pve focused players as well, and may serve to bring the community closer (more people doing the same thing).
D3 does not currently provide worthwhile PVP. There is no current focus upon changing PVP directly (although skills are being changed, and elements being added/modified - this is a step in the right direction). If/when devs decide to change PVP, it would be a lengthy process, and would be akin to starting over (it should be noted that this would be a costly change, more man hours = less profits, which is always a concern for any business). I wouldn't hold my breath, but I would really like to see my hard-earned lootz go to good use (pwning other heroes for glory, honor, and more lootz).