Moyale - Masabit - down to Archers Post is a very rough road but perfectly possible.
Risk of Samburu / Somali shifta is reasonably high. We got through without a problem and throught it was all police hype but met 4 dutch people in Nairobi who had tried to head north 2 days before and had been stopped due to being shot at, driver taken out by 15 armed men, made to lie on the ground with a gun to the back of his head. Only took £20, gave back video camera / other electronics. Travellers badly shook up, abandoned exped and shipping out.
Met a Dutch motorcyclist who hitched a ride on a lorry which also got shot at. Lorries appear to be main targets. However also met members of Royal Welsh Fusiliers down on exercise who got held up and shot at - and ther in uniform in camed up Landies so if locals prepared to shoot at soldiers then tourists are easy picking.
Perfectly possible but there is a risk. Saving grace is last week Brit government paid millions to compensate several hundred samburu tribesmen for injuries sustained due to ordenance left from Brit Army exercises that has since exploded and maimed them. So at present they are probably richer than most the travellers passing through.