I've had a few 'cool' ideas for new compositions. And I thought that I could play them alone, but perhaps that it would be more interesting (for a teacher - student situation perhaps?) to give them a little extra edge and compose them for piano - 4 hands.

Do you feel that there's an empty space for that arrangement? I don't think there are too many works and especially not too many contemporary works. From an educational point of view, it can only help, since it pushed the student to go further into syncronizing not only with him/herself but also with another person. It's easy to play, since you don't need anything else but a single piano and it can be huge fun.

Anyhow... it may seem 'commercial' but that's about it: Do you think there would be interest to such a set of pieces (for 4 hands I mean)? Just curious to what other people think about this, that's all!

I believe 4-hand playing has an undeserved reputation of stuffiness, to some evoking images of elderly ladies at tea parties. Obviously 2-piano music is more glamorous and can produce a fuller sound. But 4-hand playing is great fun and a challenge in itself, there is nothing stuffy or old-fashioned about it. Every pianist should try it. It is especially useful in teaching situations, provided you make one part significantly easier than the other.
So yes, do go ahead with that. It might be a challenge for you as a composer, too.

It never occurred to me that it would bring images of tea parties and the such.

I have a hunch (without having any musicological backup here) that the initial idea of the quatre mains works was transcribed symphonies and the such. Without an ipad/ipod/Cd player/tape player/vinyl player the only way to listen to a symphony was to... go to a concert. And that must've been much rarer than having the mp3 in your computer. So to counter that effect people used to transcribe a lot of symphonies to the piano, only that 2 hands seemed insufficient in most cases!

I've no idea if the above is correct, but it will be a challenge to treat the material I have in a right way! I think I'll go ahead with that for as long as the muses are kind with me! Then I'll carry on working the hard way!

I especially like the idea of contemporary 4-hand piano works. I'm no expert on 4-hand piano, but the most contemporary pieces that I'm familiar with are those of Rachmaninoff, and those are basically late Romantic works.

Maybe it's just my imagination. But I'm pretty sure that in the 19th century, 4-hand playing was quite the In Thing on the salons. But I've no factual backup for that, to be honest.

Yes, that's another, and very important aspect of it. For example Smetana created a 4-hand version of Ma Vlast,
one movement of which I'm working on to record together with another PS member next month. While playing 4-hand is great fun, I do find the practicing of one's own part extremely tedious, especially in orchestral music with its many unpianistic textures like extended tremolos.

Go for it ! May the Muses be with you