Make it easier to compare lists with friends. Example in the screenshot.

This should be straight forward, they have a pretty decent API: https://github.com/hummingbird-me/hummingbird/wiki/API-Reference.

Now extremely awesome would be not just import, but a sync feature (this is possible with the API). I realize you might not be interested in supporting this but I would love you for it :)

I think it would be a good idea if we could have some way to customize de display of our calendar. For example de size o it, the colours, if we want to show the images of the shows or only the text, etc..

Add hentai anime that are present on anidb.net

We have an option to see the time spent watching tv shows, animes or movies as a whole but it would be nice to be able to see time spent per tv show/anime/movie where we could then rank them based on time wasted.

Add Airing Hours in my timezone to Calendar View

I wanted to ask if it would be possible to put the site in several languages, there is this site www.localeapp.com that helps, so the users helped translate SIMKL for several languages. This is how TMDb did it. And they would gain many more users because not everybody knows how to read in English.

it's awesome you sync my Netflix history. A natural next step would be to sync my Netflix queue. My queue is large (probably 100+ titles) so a platform like simkl could really take the headache around what to watch next! it would make sense to use simkl as a launchpad!

Add symbol before title in search entries to know if it's already in the list and in which list; for example a star for plan to watch, a green circle for completed, etc.

Putting the names of each episode from a TV series in the check list.

Add a filter option in the user list such as genre, year, director, actors...

Add a field in entries where you can see the user tags

make your site more animated :D
and colorful

If a TV show has not got a Title/Descriptions in English the TV show can not be added. Sometimes TV Shows that are not English spoken, have no translation on TVDB for theirs title. The TV show should be added anyways respecting it's original title and language.

I've seen that happen to a show that has description in Spanish and English but the title is only in Spanish and Simkl refuses to recognize the show

Option to score half star (.5)

Here's an idea: you guys could add a feature through which users can plan/set goals for what and when they want to watch. For example, tomorrow I want to watch two episodes of Friends, the next day The Shining, then the day after three episodes of Attack On Titan...
Or it could also have something like: By the end of this month I want to have finished Season 3 of The Walking Dead, every Christopher Nolan movie, Full Metal Alchemist...

Suggest a TV Show/Anime/Movie to a Friend/Follower and an alert for when the friend marks it as Watched.