I think just about everything has been done at this point and honestly, not much improvement in hunting capability in the last century.
I do see the allure of designing, making and using your own cartridge and any reloader can surely identify with that type of satisfaction.
I have often thought of coming up with a cartridge of my own but am having a load of fun making bullets from old brass, which of course has been done for decades although all of these new cartridges do form a good foundation for some pretty good bullets. The 5.7X28 being a prime example. Should make great 303 bullets!