UPDATE: The sketch above isn't actually a design concept for the rumored X4. It's a design concept sketch of the X3, as little as it may resemble the final product. For now, we're filing the X4 in the "probable, but not yet confirmed" bin.

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The idea of a "sports activity coupe" to slot in below the BMW X6 isn't a new idea. It's been passing around backrooms in press events and Web forums for over four years now, popping back up as a possibility this summer. Once again it's on the radar with a report that it is actively in development, with an on-sale date sometime in 2014. Oh, and BMW is handing out official sketches of the vehicle at its 2011 X3 drive launch today.

As unnatural as the crossover-coupe may be, the X4 would be a natural progression for BMW. The X6, progenitor of the sloped-back SUV, has been very successful for the brand. Offering a slightly smaller, more efficient, more affordable version could be a recipe for a blockbuster.

So far, however, it's merely at the "it's coming" phase, according to the report. Design, styling, and specifications remain up in the air, though this official sketch gives us an idea of what to expect. When built, it will share much of its hardware with the X3, just as the X6 draws on the X5. That could mean a pair of engines, one turbocharged and one naturally aspirated, though by the time 2014 rolls around, emissions requirements may have changed displacement, power, and configuration considerably.

[BMW, Auto Week]