I'm not sure even Cityjet will have an answer to that. If it wasn't for LCY restrictions then I'd imagine they'd standardise on the CRJ.
They'll probably continue with a small fleet of Avros for the meantime to see how the EI tie in goes and what if anything falls out from Brexit.
The question will then become if they should replace the avro or pull out of LCY. Can't imagine they make that much in this day in a age to operate a subfleet of e jets or a220s just for LCY ops.