Could be quite fun depending on how deep you can get the eat/gain-ability mechanic (and you'd probably want to shoot for a balance of quantity of abilities and amount of use you can get out of them, as too much of either and not enough of the other could be quite disappointing). I would recommend a couple playthroughs of games with levels focused heavily on individual mechanics and unique gimmicks, such as Donkey Kong Country 2 or Metal Storm (NES) to help you get the most out of the abilities.
You may also (depending on how organized and analytical you are) find it helpful to list out everything you can do with each powerup and systematically make a list of every challenge and obstacle you can think of using it. It helps keep you from overusing or underusing challenges and ideas, and really fleshes out whether particular concept has as much potential as it seemed when you first thought of it.
I would also caution against using space as the primary jump button, particularly if you plan on any fast or precise platforming challenges, as space feels less responsive than most keys for often rapid-fire actions like jump (the standard in flash platforming seems to be "s" or "x"). And while on the subject, as a long time player of platformers with a keyboard, I think "down" would feel more natural for "eat" than "up" would. Neither one's really a big deal or anything, just a suggestion.
