With the blistering speeds of a couple of SSD's in raid 0 today can accomplish will likely be just standard speeds for a single disk in the coming years and when you're capable of transferring multiple gigabytes of data per second well... you can do some very interesting things. Up until now we've either had to deal with waiting on loading screens or have them hidden in the background while we do other things. Granted we've gotten much better at making them shorter and less obvious and they're not exactly going to disappear anytime soon, yet we can now consider doing things we wouldn't have considered before given that we're not as restricted. It may also come to pass that we simply load the entire game all at once when we start it up and actually do end up getting rid of loading screens, except of course the one, which would still likely be shorter than your average screen these days.
Consider that some if not most SSD's released in the last year have transfer speeds upwards of 500mb alone and easily reach 1 to 2 gb with an extra drive or two in raid 0. If future drives transfer at 2gb/s and the generally largest games of right now like max payne 3, witcher 2, etc are usually around 25gb having 15 seconds to load the entire game is comparatively short and could easily be optimized to load priority materials first getting you to the main menu and / or game much quicker. I would say that it's unlikely that game file sizes will increase much beyond that in this same near future. By the time these drives are a reality I would wager 25gb a game would still be considered quite large as the average right now is usually between 4 and 8gb with larger games like skyrim being 13gb by default before mods. This is where things start to get interesting as once you have the entire game at your disposal the question can then become what can you really do with it?
For starters provided your graphics card can keep up with it you'll be able to have substantially higher definition textures and resolutions. Larger high quality worlds to play around in will also be a likely reality. There's room for some innovation in the idea however as much good as it does it also opens an easy door to developers in a crunch in that they might not focus as much on optimizing everything.
Also consider how it might effect services like steam when you're capable of having multiple games fully loaded at a time to rapidly switch between. I'd wager to say the steam overlay might end up including a new game launcher feature down the road and games more often getting split up into sections like they do for call of duty in which single player and multiplayer are considered separate parts. If you have related games then hopping from one to another like mass effect 1,2,3 you might not want to exit and rather just skip right over bypassing the normal exit and launch steps. This might also have a mechanical advantage to game devs for some creative ideas of having multiple games running simultaneously. This might include playing a minigame puzzle while playing the main game for added bonuses or as a trial to proceed, rather than traditional boring mini games you can design a fully featured stand alone game to launch within the game. Just one of many considerations.
What it comes down to is SSD's will have you playing bigger and better games or at the very least newer games faster than ever before while opening doors to amazing potential. I'm excited just to see what I can do with the tech and how it might change game development processes.