Plenty of indications have been given over that the story-writers have explored the all current casting including Spike over 3 seasons in a fairly thorough manner. If the move is going to be permanent, then either the next season is going to turn into G3-esque episodes or the third season is going to an end for the current main cast.
One way or the other, Hasbro and the current story-writers have a lot to do with what's going on since I had a huge feeling that the season 3 was going to be the point where MLP:FiM's storyline direction was going to be entirely independent to the original concept laid out by Mrs. Faust, and judging from the current released episodes and the stuff that's on the horizon, I now have a strong reason to believe that; such is the case.
They have an entire control over what they want to do and I have no quarrel with their move. However, I don't necessarily believe that this should be the way to go as well, there's an underlying message that the end of all this is going to generate which the story-writers are not intending to make (at least I think so), but that underlying message is something I find highly inappropriate to the children based on my perspective of what the society should teach the children.