Seems to be intentional, honestly. Germinate Invoker Barbarian is clearly meant to be able to use abilities that require patience or concentration. Enlightened Bloodrager
is similarly construed to permit the user to use any spell, not just Bloodrager spells.
Other ways to cast spells while raging (aside from Moment of Clarity or casting as a Bloodrager) include the Mad Magic
feat (which requires bloodrage or perfect clarity rage power), the 1st-level bloodline power of the Vestige
bloodrager bloodline (uses a swift and halves morale bonuses, can also be obtained with the Raging Blood
feat), and Furious Spell
metamagic, which gives a +1 level penalty and a +2 to CL checks. This of course means that it is also possible to use a metamagic rod of furious spell to cast spells while raging.
Lastly, it is also possible to equip the Robes of Xin-Bakrakhan
, which is a ludicrously expensive item (198k gp) giving +1 to caster level, a +5 shield bonus (a +5 mithral buckler is cheaper), and 24 spell resistance in addition to immunity to calm emotions and the ability to use all skills and abilities that require patience or concentration when under the effect of a rage spell or similar effect.