Yes, it was EI-CBK for the past couple of days.
There isn't sufficient slack in the schedule to operate an additional rotation to either of the destinations that you mention. I'm sure they'll leave it at 3 x daily SEN-DUB for the summer, with an ATR72 substituted when loads warrant it.
I believe there has been quite a bit of interest in through bookings to the US city destinations on offer via this route, with the SEN management stressing that no such service is available from either LTN or STN.