The engine is probably going to stay the same, a 2.9-liter V6 with two large turbos pumping it up to 450 PS (444-horsepower). It's roughly the same unit they installed in the new S6 and S7. As disappointing as the loss of those V8s was, Europe suffered much worse. There, you get a 3.0 TDI making 349 PS, which is barely more than the old A6 competition.
In any case, the RS4's emissions are good enough, so all it needs is a new front end. This latest set of renderings comes from the Russian website Kolesa and shows it from both angles. This actually looks like a quick Photoshop touchup job, as the real 2020 RS4 will have new side skirts, 3D taillights, and a much more pronounced diffuser.
We speculated that, because the M3 is coming out soon, Audi was going to make a performance version. But as things stand, it doesn't look likely. Instead, the company is probably looking into more plug-in hybrid systems. There was one on the Q8 Sport concept a while back, featuring both a V6 TFSI and a big battery. Unfortunately, the RS4 is already one of the heaviest models in its class.
Other manufacturers face similar hurdles, with AMG reportedly even considering a hybrid 2-liter for the next generation of the AMG C-Class. Ouch!