The problem with Ireland potentially merging with the England cricket team is that it would sitll be called the English cricket team. Wales are apparently part of the ECB, but they are never ever mentioned. There's not even the formality of calling it the EWCB. The smaller part of a merger will always be swept under the carpet. If (and that's a big if) I ever made it to the level where I could be a test cricketer, I would never EVER play for a team under the 'England' banner. Simply because I am not English, I think that someone should play for the country they were brought up in, or maybe have relatives who lived there or something similar. I also don't agree with South Africans and Australians playing for our cricket team, but without them we would be even worse, so I have no qualms about supporting them. Just my two pence worth.
EDIT: Just on the topic, we are nowhere near ready for test status. I think we should have a first class infastructure in place before we can even think about test cricket. Making teams for each of the 4 provinces (Ulster, Munster, Leinster, Connaght) could work.. and If we could provide a high-quality first class competition and be competitive with other nations (Maybe playing international sides 'A' teams), then we can consider test cricket. But for now, no way are we ready.