That is what spin offs are for. Let it be an independent company that you still own 49% of. If it fails, at least you got to sell the 51% stake first. If it succeeds, you still own 49% of it.
That doesn't solve the underlying problems of profitability and minimal bottom line impact. A $100M company is unlikely to be profitable for several years, during which time Google has to spend money to get it off the ground and suffer a brain drain from existing profitable products to an unproven subsidiary. Meanwhile, "success" here would still mean < 1% impact to anything shareholders care about... years down the line. It makes more sense to just add some funding to Google Ventures.
