Typesetting a computer-science book with XeLaTeX+biber
I haven't done with the svmono but I just had to tweak another publisher class to use lualatex and so after a quick look at svmono I would say
I would prefer lualatex over xelatex due to the microtype capabilities and better graphic (pgf) support (and it is now faster than last year due to changes in expl3 and in the font loader).
I would expect 2-4 hours of work to move svmono to lualatex+biber, where most of the time is needed to check the code and consider if it could be problematic or not (mostly there will be no need to change something).
I wouldn't expect large problems, but would still expect to have to adjust small things later as one always overlooks something in such rather old classes ...