Assuming the RS doesn't vomit driveline parts... Marketing and real life are often two different things. Nothing money can't over come ( ask the EVO and STi boys ). But to say we can be sure the driveline will be built proof is going a little far. Also, most focus ST's are 3450lbs. The RS will add a good 250lbs. Now we're talking 3650-3700lbs !!! And I mean on a scale, not on a door sticker or sales pamphlet. A 350hp AWD car that weighs 3600lbs will still be fast/quick. But its not gonna be an instant 11sec car. One that runs 11.50 would likely be on the bring of exploding a VERY expensive driveline, if it had not already exploded.
Power + weight + AWD is rarely a combo known for reliability, and if it is reliable ( see AUDI ), then its rarely ACTUALLY fast ( which is different than magazine fast, again, see EVO/STi ).
One more thing... Guys that have been around the fist for 2+ years now, we know how hard it is to bring parts builders around for a low production car, how do you think that will apply to the RS with 70% of people buying them say, "I have an RS at home in the garage, I check the tire pressure 2 times a week, but never drive it". The other 30% might drive it, but modding them maybe not be a real thing for 5 years ( see 2004 R32 VW golfs ).
Don't get me wrong, DHM will prob have a setup for those 1% of people that are not going to be ok with losing to a fiesta at the drag strip or getting COMPLETELY DESTROYED by a big turbo Fost on the highway, but I just don't think modded RS's are going to be very common with the price and resale they will have.
On the flip side, the price of a 2013 fost is about to fall into SRT4 land, lol.
I do have to agree on the point of fiesta's ans even fost's not driving around on slicks everyday. Fearthesnail vs a stock RS on the street 0-100mph ? My money is on the RS that is likely a 13.50 car, lol. My good friend has a 28k mile 600hp syclone, and awd on the street is about impossible to overcome unless is a wrx, lol