I worked on something similar a week ago.
First of all, I didn't finish it by beeing not clear enough about the rules.
Then, this doesn't work exactly as you said: Heighten only works up to level 9 spells. So you can take 6 feats for extra slot and then have a slot of each spell level (3rd to 8th). Now some questions:
1. Do you gain additional spell slots at level 3-8 for having high attribute?
2. Do you gain additional spell slots at level 3-8 for being a specialist wizard?
3. If you gain additional spell slots by one of the above, could you then use Dark Chaos Feat Shuffle again to retrain your extra slot-feats into fighter feats, loosing the slot but keeping the "additional" spell slots?
/edit: by the way, some additional ways for "free heighten": Illumian with Improved Sigil: Krau, Easy Metamagic, Metamagic School Focus, but best of all: the level 3 ability of Magical Trickster (+4 spell levels) and the capstone of Anima Mage (hard to get :/, but it's free Heighten spell to level 9).
@Soro: I don't really get your question
but I think the answer is no.
Even if you need to keep the Extra Slot feat, you can go broad in dual casting.
Illumian Conjurer 1/Sorcerer 1/Shadowcaster 1/Spellthief 1/Magical Trickster (improving sorcerer+2) 3/Shadowcaster +2/Nocturmancer 10 (sorcerer+10)/Incantatrix (sorcerer+1) 1
level 1 feat+flaws: Heighten Spell, Metamagic School Focus: Conjuration, Easy Metamagic: Heighten Spell
level 3 feat: Improved Sigil: Krau
level 6 feat: Extra Slot (for wizard): 4th level spell
level 6 bonus feat: Practical Metamagic: Heighten Spell
level 8 bonus feat: Extra Slot (for wizard): 8th level spell
level 9 feat: Master Spellthief
now you swap out via Dark Chaos Feat Shuffle Metamagic School Focus, Easy Metamagic, Practical Metamagic, Improved Sigil to gain Extra Slot: 3, 5, 6, 7. Also swap Heighten Spell for Quicken Spell.
level 12, 15 and 18 feats should be Practised Spellcaster (Wizard and Sorcerer), Extra Slot: 2
level 13 bonus feat should be Extra Slot: 1.
At level 15 you retrain the Wizard level for a new Shadowcaster level, using the rules of ToM. At level 19, you take Iron Will as a bonus feat. Take Empower as bonus metamagic feat at level 20.
So you end up like that:
Shadowcaster effective level is 14, thus he got level 7 mysteries.
Wizard effective level is 0, but has spell slots of level 1-8 and a CL of 26.
Sorcerer effective level is 14, thus having level 7 spells and a CL of 26.