My views as someone who departs DUB weekly.

Downsides
T1 security is quicker than T2 (only comparing Fastrack)
The Red car park bus is much easier to catch from T1
The T1 lounge has better food than the EI lounge or the PP lounge in T2

Upsides
Hopefully we will get airbridges for BA in T2, this will make a difference in winter
Not having to board LCY flights from the overcrowded marquee will be nice
If LCY flights depart from the bus gates where Emerald Air go it will be a VERY poor experience.
Fewer people getting lost in the maze of corridors on the way to immigration