Even though I really like EMI and use it a lot, I am a bit nostalgic about REI feature for grouping items. Yes it needed to be done by hand by writing a bit of code, but in the end i was able to group similar items (like colored wool, buttons and such) into the same item so it doesn't waste space on the panel and i could expand and collapse when needed.
Will similar feature come to the EMI? I believe it would be very handy for people who have a lot of mods installed or want to clean their item list. I haven't seen this feature in the docs so i decided to submit a feature request. I also understand such a feature would be very hard to implement, especially if you go all user friendly and allow users to create groups inside the game (which is like a very good feature for many reasons as users don't have to leave the game and can tidy up their cluttered panels especially when there are lots of mods) unlike REI does.

Emi already stated that she does not intend to include other’s original ideas like item grouping in EMI, it would be very handy but it’s understandable that she wants EMI to be its own original project.

If you really want it, you could develop an addon for EMI that adds the functionality

That's a very strange stance. No single mod holds a monopoly on general features, such as item grouping. And not including some features just because it makes you a bit more similar to another mod only limits your own mod and doesn't really achieve anything meaningful.