This idea is very good,especially for outdoor duel filming,with lots of daylight,using a big light close to camera.
A fx saber,even with a 100w led blade won't get bright in daylight,especially with sun,like today,will just appear as a white pastic stick...
So I bought colored tcss blades,to have color under daylight,to have easy rotoscoping.
But you idea is far better,because used in good condition,it can even give a realistic look,maybe without any rotoscoping...
These days,I think about many ideas for "easy fx" for filming:reflective tape as yours,fx saber but shor blade,or without blade,duelleble versions,springing blade with magic cane,for instant blade opening,depending on conditions,both can be interesting...Especially for a obiwan saber,match all filming conditions,it's a really hard challenge.