Generally this type of mechanic is present in MMORPGs where the class' balance depends on this sort of thing. With Sindome's classless structure, I don't believe it's necessary.
Realistic, yes, but possibly unbalancing, and likely to encourage players who otherwise wouldn't be the sneaky types to take it just for the advantage it would bring to combat.
Right now the advantage to being sneaky is, as with sniping, the ability to not only pick your target, but to pick the time and location as well. That, in itself, and with the right people, is a powerful advantage already.
Maybe the GMs and other players would disagree though. I dunno. Just my thoughts on the matter.