Learning new words isn't that hard - it's learning new characters that's hard. With this in mind, it'd be a great feature if memrise was able to look at the characters you already knew, and suggest words that you might like to learn, which are made up of those characters. For days when you're feeling like you can't cram much new new stuff into your brain, perhaps.
Mind you, for this to be useful, it would probably have to refer to character-frequency lists to prevent obscure and irrelevant suggestions. Still, I'm pretty sure there are freely-available frequency lists out there that don't require licensing etc.
Perhaps even more useful would be a similar facility to suggest words that feature characters you've already learnt - but for which you don't know any 2-character combinations. e.g. I might know 参 but not any words featuring it. (This shouldn't happen much with really well-curated lists, but it does occur from time to time). Or just a facility like 'suggest words with character X'. This would be particularly helpful for problem words, as each combination gives you another chance to learn, and another associative hook to hang it on.
I'm really just thinking aloud here - none of this is top-priority stuff, but might be useful to put in the 'future ideas' file.