It can be done in war time as well -- if one is winning as were the Allies in Europe 1944-45. Whether it can be safely done in other aspects of major war is arguable.

The real issue is not whether it can be done -- as most anything can be if one wants it badly enough -- the issue is should it be done. I'd say for a small well trained Army under most circumstances it makes a great deal of sense. For a large, mobilizing Army, perhaps a little less sense. There is also the issue of affordability; all well and good to train broadly but if either time or funds or constrained, it may be inadvisable to train soldiers in skills they may never use...

A point to recall is not the raw skills, they're easy -- it's the cognitve skill enhancement and, even more importantly, muscle memory that become important to survival and success in intense combat and that argues for specialization.

Yet again, it's a METT-TC and situational issue -- there is advisedly NO one size fits all in warfare.