congrats to your website!
I am German and trying to learn Russian.
Good mems are still rare. And Mems are the corner stone of an effective learning the vocabulary.
I have a few suggestions to boost the use and development of Mems by the user-community:
As far as I overview the allocations of Mems, its only course concentrated. So there may be good Mems in another course which the user cannot see. It would be helpful to interconnect Mems between the courses. It could be helpful if the user of them Mem could decide this, due the dependency of context.
Even further it could be helpful to be able (for the user) to decide if a Mem can also be used - not only by his (mother) language but also be others tongues. I suppose this could be especially helpful for English speakers.
It might be helpful - as soon as several Mem options are present - to let the users vote on there effectiveness, so that the best Mems could be suggested at first. I can imagine that a rating by users could stimulate others users, to do there best for good mems.
A helpful feature for users could also be the ability to search for Mems in a special search. For example you search for a particular word and see if a Mem for learning has already been made.
In the Russian courses provided by Memrise - an option to the spelling with the Cyrillic letter (instead of the phonetic Latin letters) would be nice - or just to be able to block out the spelling part.
For the individual use / or unfinished Mems - it may be helpful to have the possibility to decide, at which point the Mem goes public.
A nice feature would also to be able to print the Mems as a flip card.
I`d love to hear if you are considering such or different features to improve the great learning experience on your website - knowing that some of the above topics have been already discussed.