To be honest, I do not think that MCGamer will lose many people at all. We've gotten rid of support for 1.5, 1.6, and now 1.7. In all of those, people were upset and complained; however, our player counts showed little change. After all, MCGamer has logged about 3.1 million people on at some time or another.
Also, adding on: The most popular complaint is that there will be lag. Perhaps the lag is because MCGamer is supporting both 1.7 & 1.8 right now. Once support for 1.7 is dropped, maybe it wont be so bad. I don't know, but please take this into consideration.