Let's do a quick comparison:
1) Crossblooded sorcerer is at an advantage when it comes to bonus feats (oracle doesn't gain any, unless you count some revelations) and arcana (oracle doesn't get this).
2) Both are even when it comes to the pool of bonus spells (oracle gains them one level earlier, but that's minor).
3) Dual-mystery oracle is at an advantage when it comes to class skills (they gain usually 4 per mystery) and revelations (choosing almost at will from a huge pool, with Extra Revelation feat possible).
IMO the dual-mystery oracle has an edge thanks to revelations, so I'd increase the drawbacks somewhat. Maybe an additional -2 to Fortitude.
If I were creating this custom archetype, this is how I would do it:
It is rare that those cursed with the power of an Oracle emerge into the annuls of history, and rarer still when a singular Oracle bears the burden of two curses which grant them heightened powers. Then, there are those which bear a gift so powerful that the universe itself attempts to enforce a balance. This could be due to many different reasons, such as powerful divine forces attempting to increase their influence in the mortal realm, the return of an old and powerful soul to the realm of the living, the unnoticed machinations of elder beings beyond the outer realms, or many other possibilities. The result is generally the same; an oracle awakening a connection to more than one Mystery and accessing Revelations from both.
Restrictions: This archetype may not be taken with any other Oracle archetype.
Oracle Mystery: A dual-mystery oracle selects two mysteries at 1st level.
Oracle’s Curse: A dual-mystery oracle must choose two curses at 1st level. One of these curses (oracle’s choice) only provides them with a drawback, never a benefit, and functions only to hinder their development. The other curse comes with its normal benefits.
Class Skill: A dual-mystery oracle receives the bonus class skills from both of her bloodlines. If these are the same skills, this does not grant any additional benefit.
Bonus Spells: A dual-mystery oracle may select her bonus spells from either of her mysteries. The oracle also has the choice to learn a lower-level bonus spell she did not choose in place of the higher-level bonus spell she would normally gain. Lower-level bonus spells learned this way always use the spell level that they would be if the oracle had learned them with the appropriate bonus spell.
Bonus Revelations: A dual-mystery oracle gains a new revelation at 5th level and 13th level. These are in addition to the normal revelations she receives at 3rd level, 7th level, and so on.
Revelations: Each time a dual-mystery oracle may select a new revelation, she may selection any one of the revelations available to her at that level for either of her mysteries.
Drawbacks: A dual-mystery oracle has one fewer spell known at each level (including orisons) than is presented on the oracle spells known table. Furthermore, the opposing natures of the dual-mystery oracle's dual curses constantly take a toll on her being. This leaves her in constant strife with resisting the fabric of the universe's constant attempts to impose a balance to her growing power. A dual-mystery oracle takes a -1 penalty to all saving throws.