Warlock is one of those archetypes that many people really want to make work but it fail short. It just need that little something that pushes it up from mediocre to viable. There are many sources to take inspiration from but you have to be a real text-lawyer to dig through and understand all the pit traps in this otherwise fascinating class.
Here's what I've compiled after digging through the internet and Pathfinder FAQ.
Mystic Bolt can be selected as a Weapon for the purpose of qualifying for Feats such as Weapon Focus and Improved Critical.
Mystic Bolt is not a manufactured weapon so you assume first that effects like Haste or Sense Vitals do not work but FAQ specifically name state that haste do indeed work with Mystic Bolt (thanks for that). Nothing official about Sense Vitals as far as I've seen.
Mystic Bolt (as described in ability text) can be combined with:
two-weapon fighting
improved two-weapon fighting
greater two-weapon fighting
Rapid Shot and many shot is trickier. Rapid shot require a "ranged weapon" and mystic bolt qualify as a "light one handed weapon", it however can be used at range, so the correct term would probably be "ranged light one handed weapon". Rapid Shot should work if that assumption is correct. Manyshot however specifically state "bow" and "arrow" which is pretty clear.
Same with Point Blank Shot. It require a "ranged weapon" so if mystic bolt at range qualify as "ranged light one handed weapon" it should work.
Arcane Strike work as per described in Pathfinder FAQ. Not too hard to figure out though. It affect weapons and Mystic Bolt count as a "light one handed weapon".
Deadly Aim, Piranha strike and Power Attack doesn't work when Mystic Bolt is used at Range against Touch AC. Power Attack for example will probably work at melee if it target normal AC.
Some try to multiclass to get around the fact that Mystic Bolt scale horribly. Arcane Trickster being one of the top candidates where you combine spellcasting scaling with sneak attack. However that combination just seems to be straight up worse than a standard Arcane Trickster.
Then we get to Lethal Grace. The ability that would make Warlock viable. It states: "When using Weapon Finesse to make a melee attack using his Dexterity bonus on attack rolls and his Strength bonus on damage rolls". First part is is easy, damage would be added on melee mystic bolts, not ranged mystic bolts. Second part completely block this ability since FAQ state that Mystic Bolt does not add strength to damage. It feels like RAI is to deny this talent from dex-to-damage builds, not mystic bolt though.
Summarizing everything. Warlock ranged touch attacks at level 10 could consist of six attacks. (2 from BAB, 2 from two-weapon fighting, 1 from Haste and one from Rapid Shot). Each attack deal 1d6+6 (normal scaling, arcane striker and point blank shot). If every attack normally hit and deal average damage. Mystic Bolt would deal 57 damage. More realistically ~2 attacks is likely to miss reducing the damage down to 38. Other classes reach that level of damage 1-5 levels earlier (kineticist is extremely strong at level 5). Note that this is a build that focus entirely on increasing damage, there is no room for utility and fun. Everything goes toward increasing damage. Giving Mystic Bolt just a tad bit more damage is what it needs to go from below average to balanced.
What do Paizo say about the matter? Is it indented that Lethal Grace should not be used by an archetype of the same class? Is Sense Vitals intended not to work with Mystic Bolt? Have the community missed something vital for Warlock builds to work?
