expansion pipe allows for more efficient fuel burn - burning unburnt fuel via pulses.
my assumption would be direct injection can inject multiple bursts to simulate exhaust pulses. but without a chamber how would it 'supercharge/compress' the air as a chamber does?
or maybe i'm way off
anyways, i would think that gasgas would eventually have direct injection - they did hire Pierluigi Marconi who headed up the design team of the ill fated bimota v-due.... i'm assuming he's still there - i believe he designed the side valve trials motor.... there are several direct injection motors on the market - the e-tec being one of them...