I am not sure you can get quite to 100, but you can probably get very close. It is a question of how much time and money are you prepared to put into the phosphors, and how low an overall efficiency are you willing to live with. Since Energy saving (total cost of ownership) is what drives the LED lighting market, very expensive low efficiency LED's aren't likely to be very popular, so today the market for such a device is simply too limited for manufacturers to make such a product.
For example GE used to make 5000K F40 Fluorescent lamp with a CRI of 96 IIRC (Chroma 5000 series). It was fairly expensive, and had about half the lumens per watt of the 'best' F40's, in fact the performance was so poor that the lamp was discontinued because it could not meet the mandated efficiency standards. While your average Home Depot F40 cool white Fluorescent is about $1, the high performance, high CRI fluoros like the GE SPX line are more like $7-$8 each at wholesale by the case. the market for these lamps is fairly limited, while they provide excellent color rending (and are ideally suited for some 'high end' applications, they are too expensive for general use.