There is nothing wrong with the idea. However I do not think it will get too much traction. 

First there is no difference in emission for the first 4 years. So for a long time there is nothing that sets it apart. Then I am not convinced how many active developers will support it. If they just copy commits they will always lag behind. Finally, Grin is already experimental. I do not see a fork at this point get many people using it. 

Instead I think that IF GRIN is a success that we may have a bitcoin-like fork in 2-3 years from now when the first having would be due.