I am not surprised that no LCC dares to cross the pond. They simply could not compete with the existing airlines. Even if they just charged Euro 300 for a return ticket, they would be not significantly cheaper than the "full" service airlines.
However, the LCC would only get you from A to B (let's say FRA
), however you want to go/have to go from C to D (STR
). The existing carriers fly to you from C to D for the same fare as from A to B.
Meaning, whatever amount you would save on the trans-atlantic portion, you would have to spend (perhaps even considerably more) on the domestic portions of your trip.
In addition that that, just imagine Ryanair decided to start a service from Hahn (right in the middle of nowhere ... but no big deal because Germany is so small, so you can there easily) to a similar place in the US of A. Fine, you are in the States - but want on earth do you want to do right in the middle of nowhere?
Above said also explains why there are hardly any "charter" services across the Atlantic left. Think of all the routes German charter airlines operated in the past. Most of the remaining services are to Florida - and cater mainly to tourists (and even these flights are not considered charter anymore).
Personally, I don't think a fare of EUR 100 o/w is realistic. Operating long haul flights would add considerably to crew costs. For each city pair (if served on a daily basis) you would need one plane ... plus back-up capacity, making scheduling much less flexible than on existing LCC routes.
So, as I see it ... we won't see any LCCs plying the Atlantic in the foreseeable future.