Terrible Mistake
The PC business was so price-competitive, IBM risked compromising its reputation for quality by staying there. In the case of servers, X86 benefits from the large desktop market bringing down prices - whereas the PowerPC and the z/Architecture platforms do not. So it would be a huge mistake to be left only with non-competitive entries in the server market; a niche premium-price market will in time shrink, even if it's profitable for the moment.
Instead, IBM should be looking at the declining PC market and the surging laptop market, and the demand for energy efficiency, and it should add a lineup of ARM servers to its offerings sometime in the near future. It doesn't have to be the first - in fact, some other companies are already doing it - but when the ARM server makes sense, IBM should be there.