In short, I don't think the "deliver in 3 days" rule will have any effect on individual traders - it simply changes how your broker has to handle the trade afterwards. The exception is that, for some brokers, who are not already clean about this, it may reduce the size of their shortable stock list.
What's with the mention of ARCA and Island having less stringent short rules? That got "fixed" a long time ago. If anything, Island (as well as INCA) is more restrictive now by not allowing short sales below the previous NYSE closing price during after-hours and pre-market (in listed stocks anyway).